cgit_open_filter: hand down repo configuration to script

cgit_open_filter: hand down repo configuration to script

The environment variables can be used to (for example) resolve
the following situation:

Suppose a server setup in which each repository has a trac
instance; the commit filter needs to know with which
repository it's dealing in order to be able to resolve the
#123 ticket numbers in the commit messages into hyperlinks
into the correct trac instance.

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>