index: stage an unregistered submodule as well

Handle ssh:// and git:// urls containing a '~' character.

For such a path '/~/...' the leading '/' is stripped so the server will
get a path starting with '~' and correctly handle it.

We previously added logic to `_add_bypath()` to update a submodule. Go
further and stage the submodule even if it's not registered to behave
like git.

When we pass the path of a repository to `_bypath()`, we should behave
like git and stage it as a `_COMMIT` regardless of whether it is
registered a a submodule.

Resolve documentation warnings

Remove extra semicolon outside of a function

Without this change, compiling with gcc and pedantic generates warning:
ISO C does not allow extra ‘;’ outside of a function.

iterator: skip over errors in diriter init

case-insensitive check for WWW-Authenticate header

Fixes issue #3338

We don't want the iterator to make us stop whenever we hit an unreadable
dir. We should instead move over to the next item.

An error here will typically mean that the directory was removed between
the time we iterated the parent and the time we wanted to visit it in
which case we should ignore it.

Other kinds of errors such as permissions (or transient errors) also
better dealt with by pretending we didn't see it.

Normalize submodule urls before looking at them

Allow adding a submodule through git_index_add_bypath

refdb: delete a ref's reflog upon deletion

filter: make sure to close the stream even on error

Make libgit2 work on Windows Vista again

Increment `git__n_inits` before doing `init_once`.

Fixes #3318.

(fixes issue #3316)

Signed-off-by: Sven Strickroth <email@cs-ware.de>

Document git_fetch_options struct and fix typo.

git_fetch_options was missing from the API docs because it lacked a
documentation comment above the struct declaration.
I used the git_checkout_options docstring as a template.

Also fixes a typo in git_remote_prune_refs (remote, not reamote).

Fix macro redefinition warning

List a submodule only once when the path matches a submodule in the index

Extract the backslash-to-slash conversion into a helper function.

examples: modernise the fetch example

Our path functions expect to work with slashes, so convert a
path with backslashes into one with slashes at the top of
the function.

The header src/cc-compat.h defines portable format specifiers PRIuZ, PRIdZ, and PRIxZ. The original report highlighted the need to use these specifiers in examples/network/fetch.c.  For this commit, I checked all C source and header files not in deps/ and transitioned to the appropriate format specifier where appropriate.

Under normal conditions, git_remote_fetch() should be the only function
used to perform a fetch. Don't let the example lead people astray.