Introduce git_reference_shorthand

Generate a shorthand name out of the full refname.
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
Make git_index_read_tree preserve stat cache

Instead of just blowing away the stat cache data when loading a
new tree into the index, this checks if each loaded item has a
corresponding existing item with the same OID and if so, copies
the stat data from the old item to the new one so it will not be
blown away.
Merge pull request #1630 from arrbee/index-read-tree-preserve-stat-cache

Make git_index_read_tree preserve stat cache where possible