ZX2C4 specific patches.
CGIT-0.9.2

Features:
- update to git v1.8.3.
- expanded set of default filters to include markdown, restructuredtext, and
  man pages.
- better sample configuration file in man page.
- "readme" may now be specified multiple times, and cgit will choose the first
  one it finds.
- "readme" no longer needs a branch name. If prefixed with simply ":" it will
  use the default branch.
- "branch-sort" allowing branches to be sorted either by "age" or "name", for
  kernel.org.
- "enable-index-owner" allowing the owner column to be disabled in the index
  page.
- print submodule revision next to submodule link.
- integrate more closely with git apis, such as strbuf.
- rely on git test harness and git makefiles.
- more robust test suite.
- more rebust makefile dependency accounting.
- pager navigation is now unordered list.
- span tag wraps commit directions.

Behavior changes:
- HOME is no longer passed as an environment variable to any filter api
  scripts.
- "about-filter" now receives the filename being filtered as argv[1]. This may
  disrupt existing scripts, so adjust accordingly.
- gitconfig and gitattributes are no longer loaded from any system directories
  or home directories.

Security:
- CVE-2013-2117: disallow directory traversal when readme is set to filesystem
  path.

Bug fixes:
- ssdiff now correctly manages tab expansion.
- support unannotated tags in http git clone.
- lots of cleanups of global variables and memory leaks.
- do not rely on gettext/libintl.
- better C standard compliance.
- make several functions and variables static.
- improved constification.
- remove unused functions.
- fix colspan values to correct width.
- fix out-of-bounds memory accesses with virtual_root="".
- cache repo config more precisely.
- die when write fails.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>