Fixed "command" from other authkeys breaking authkeys file parsing

The regexp will remove command or other options at the start of each
lines from the authkeys file. The remaining part of the line should be
the public key only without any other ssh options.

Note that it will only detect on authorized_keys file for protocol 2
(but who use protocol 1 anymore?)
Support custom Git binaries location

Added config key GIT_BINDIR to support custom Git location. The content
of this key is added to the PATH environment variable if it's present
in the configuration file.
Rewrote update-gitweb-access-list in perl

The previous version as a shell script spawned too many processes. In
a shared hosting env with limits on the number of process, a perl-only
solution would be less prone to hit this limit. Furthermore, I believe
this is more efficient than a shell script.
Merge remote-tracking branch 'github.com/sitaramc/gitolite/master'
Allow multi-valued keys in config

Implements support multi-valued keys in repository config, for instance
"gitweb.url". The keys that are treated as multi-valued must be declared
in the rc file in the GIT_MULTI_CONFIG_KEYS value (which use the same
syntax as GIT_CONFIG_KEYS)

Also fixes a "bug" in git: removing the last value of a section does not
remove the section itself; adding again a key to this section duplicates
the section name (or triplicate, or etc.)