parsing.c: make commit buffer const

This will be required in order to incorporate the changes to commit
buffer handling in Git 2.0.2.

Signed-off-by: John Keeping <john@keeping.me.uk>
git: update to v2.0.3

This is slightly more involved than just bumping the version number
because it pulls in a change to convert the commit buffer to a slab,
removing the "buffer" field from "struct commit".  All sites that access
"commit->buffer" have been changed to use the new functions provided for
this purpose.

Signed-off-by: John Keeping <john@keeping.me.uk>
ui-stats.c: set parent pointer to NULL after freeing it

We do this everywhere else, so we should be doing it here as well.

Signed-off-by: John Keeping <john@keeping.me.uk>
cgitrc.5: we mean a cgi response, not request
Always check if README exists in choose_readme()

Specifying a nonexistent README file via the readme option is sometimes
useful, e.g. when using scan-path and setting a global default.
Currently, we check whether there is only one option in the readme
option and, if so, we choose that file without checking whether it
exists. As a consequence, all repositories are equipped with an about
link in the aforementioned scenario, even if there is no about file.
Remove the early check for the number of keys and always check whether
the file exists instead.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>
git: update to v2.0.4

No CGit changes required.

Signed-off-by: John Keeping <john@keeping.me.uk>