Auto-detect the base URL that will be used by env.abs_href, using the reconstructed URL from the req, in case `[trac] base_url` was not specified.
Auto-detect the base URL that will be used by env.abs_href, using the reconstructed URL from the req, in case `[trac] base_url` was not specified.

Closes #3965.

git-svn-id: f68c6b3b1dcd5d00a2560c384475aaef3bc99487@6264 af82e41b-90c4-0310-8c96-b1721e28e2e2

moreati/trac-gitsvn,dafrito/trac-mirror,dokipen/trac,dafrito/trac-mirror,dafrito/trac-mirror,dafrito/trac-mirror,exocad/exotrac,dokipen/trac,moreati/trac-gitsvn,moreati/trac-gitsvn,dokipen/trac,exocad/exotrac,exocad/exotrac,moreati/trac-gitsvn,exocad/exotrac