Introduce git_reference_shorthand

Generate a shorthand name out of the full refname.
thread: fix segfault on Windows 64 bits

`lpExitCode` is a pointer to a long. A long is 32 bits wide on Windows.

It means that on Windows 64bits, `GetExitCodeThread()` doesn't set/clear the high-order bytes of the 64 bits memory space pointed at by `value_ptr`.
Merge pull request #1622 from yorah/fix/thread-segfault

thread: fix segfault on Windows 64 bits
remote: make default tag retrieving behaviour consistent

Default for newly created remotes will be auto.
Default when loading existing remotes with no tag retrieving behaviour set, was already auto.
Proposal to handle default value (auto = 0)
Build with the system's http-parser installation if available
Merge pull request #1530 from veeti/http-parser

Build with the system's http-parser installation if available
Merge pull request #1623 from yorah/fix/tag_auto

remote: make default tag retrieving behaviour consistent
Merge pull request #1559 from carlosmn/ref-shorthand

Introduce git_reference_shorthand
Added support for setting transport flags (No check SSL cert) to git_clone call.
Merge pull request #1621 from NHDaly/clone_transport_flags

Added support for setting transport flags (No check SSL cert) to git_clo...
improve test for index extension truncation
Merge pull request #1626 from ethomson/index_ext_truncation

improve test for index extension truncation