Refactor checkout into several more-sensible
entry points, which consolidates common options
into a single structure that may be passed around.

Includes unfinished win32 implementation.

Also removes the unnecessary check for filter 
length, since git_filters_apply does the right 
thing when there are none, and it's more efficient
than this.

libgit2.pc.in: also switch to LIB_INSTALL_DIR

b3237ac3 changed CMakeList.txt to use the more standard LIB_INSTALL_DIR
variable instead of INSTALL_LIB, but forgot to change libgit2.pc.in etc.
accordingly.

Add support for the more standard LIB_INSTALL_DIR variable

Pevents collisions with the original libgit, which also exports those
exact symbols.

Fixes #822

Not all delta bases are available on the first try. By delaying
resolving all deltas until the end, we avoid decompressing some of the
data twice or even more times, saving effort and time.

Removed 'bare' option from test repository to 
allow checkout tests.

The correct way to advertise out capabilities is by appending them to
the first 'want' line, using SP as separator, instead of NUL as the
server does. Inconsistent documentation lead to the use of NUL in
libgit2.

Fix this so we can request much more efficient packs from the
remote which reduces the indexing time considerably.

More revparse <3

refs: fix a memory leak

    passing 0 to git_strol(32|64) let the implementation guess if it's
    dealing with an octal number or a decimal one.

    Let's make it safe and ensure that both 'HEAD@{010}' and 'HEAD@{10}'
    point at the same commit.

khash.h was globally #define'ing "inline" which messes with
other files.  Let's keep it as "kh_inline".

Some objects were added in another PR

odb: add git_odb_foreach()

Fix revwalk email parsing

Revparse refactoring: a start