Various warning cleanup and minor fixes

Minimize regex usage

The git_buf_text_gather_stats call returns a boolean indicating if
the file looks like binary data.  That shouldn't be an error; it
should be used to skip CRLF processing though.

'del' instead of 'delete' for the poor C++ users

This replaces some git_buf_printf calls with simple calls to
git_buf_put instead.  Also, it fixes a missing va_end inside
the git_buf_vprintf implementation.

The attempt to "clean up warnings" seems to have introduced some
new warnings on compliant compilers.  This fixes those in a way
that I suspect will also be okay for the non-compliant compilers.

Also this fixes what appears to be an extra semicolon in the
repo initialization template dir handling (and as part of that
fix, handles the case where an error occurs correctly).

In revwalk, we are doing a very simple check to see if a string
contains wildcard characters, so a full regular expression match
is not needed.

In remote listing, now that we have git_config_foreach_match with
full regular expression matching, we can take advantage of that
and eliminate the regex here, replacing it with much simpler string
manipulation.

Fix typo in documentation

Make it pair up with the one for commits. This fixes #1691.

Fix warning

OSX 10.8 + Valgrind

Make init.templatedir work

indexer: check the packfile trailer

The packfile trailer gets sent over and we should check whether it's
correct as part of our sanity checks of the packfile.

Configurable template dir for Win32

Alternative proposal for filter API

This updates clar to the version without cl_assert_equal_sz and
then adds a new version of that macro the clar_libgit2.h.  The new
version works around a strange issue that seemed to be arising on
release builds with VS 10 64-bit builds.

This contains a few bug fixes and some header and API cleanups.

The main API change is that filters should now use GIT_PASSTHROUGH
to indicate that they wish to skip processing a file instead of
GIT_ENOTFOUND.

The bug fixes include a possible out-of-range buffer access in
the ident filter, a filter ordering problem I introduced into the
custom filter tests on Windows, and a filter buf NUL termination
issue that was coming up on Linux.

This adds more tests of filters, including the ident filter when
mixed with custom filters.  I was able to combine with the reverse
filter and demonstrate that the order of filter application with
the default priority constants matches the order of core Git.

Also, this fixes two issues in the ident filter: preventing ident
expansion on binary files and avoiding a NULL dereference when
dollar sign characters are found without Id.

Fixed the filter order to match core Git, too.

This test demonstrates an interesting behavior of core Git (which
is totally reasonable and which libgit2 matches, although mostly
by coincidence).  If you use the ident filter and commit a file
with a garbage ident in it, like '$Id: this is just garbage$' and
then immediately do a 'git checkout-index' with the new file, Git
will not consider the file out of date and will not overwrite the
file with an updated $Id$.  Libgit2 has the same behavior.  If you
remove the file and then do a checkout-index, it will be replaced
with a filtered version that has injected the OID correctly.

There were a lot of places in the test code base that were creating
a commit from the index on the current branch.  This just adds a
helper to handle that case pretty easily.  There was only one test
where this change ended up tweaking the test data, so pretty easy
and mostly just a cleanup.

These are a couple of new clar helpers for testing that a file
has expected contents that I extracted from the checkout code.

Actually wrote this as part of an abandoned earlier attempt at a
new filters API, but it will be useful now for some of the tests
I'm going to write.

I wish MSVC understood that "const char **" is not a const ptr,
but it a non-const pointer to an array of const ptrs.  Does that
seem like too much to ask.

The global and system config could interfere with the filter
tests by imposing CRLF filtering where it was not anticipated.
This better isolates the tests from the system settings.

This ports over some of the tests from
    https://github.com/libgit2/libgit2/pull/1683
by @yorah and @ethomson