[Users] BRANCH route support

Hi everybody, I just finished adding support for BRANCH routes. The idea and frame were partial ported from SER (thanks to Juha for extracting and adapting patches). For those who are not familiar with this concept: branch route is a route to be execute separately for each branch before being sent out - changes in that route should reflect only on that branch. I say partial because the features, implementation were improved. Shortly here is a list: - remove from grammar default BRANCH ROUTE definition - since this is a 100% TM route, make no sense - RURI may be changed from a branch route (the routing will accordingly change); This capability is essential, since there are core function which alter the RURI, functions which cannot be blocked in specific route types - not handling this, may easyly lead to memory faults or leaks. - flags per branch - if flags are changed in branch_route, the change will not be visible for other branches, but it will be visible for all replies of that branch (it might be useful for per branch NAT traversal) - full AVP support in branch route - more efficient handling of lumps (changes in request) - instead of cloning and removing the entire lump tree for each branch, using lump flags, after each branch, the original lump tree will be just cleaned only what was added during branch route will be removed). still pending: how to handle append_branch() core function.....I will prefer to handle properly all core functions, since their execution cannot be banned from specific routes. For the moment only textops, avpops and xlog modules were enabled for branch route. Other will come in the future. regards, Bogdan PS: testing done only superficial (is quite late now).....any help/reports are welcomed :D