(svn r3908) Fix last commit (I'm saying that way too often *sigh*) (Pointed out by Celestar)

(svn r3907) Replace many bridge related direct map accesses with calls to shiny new functions and mark some strange constructs with XXX

(svn r3906) Before removing a rail/setting the owner of a road to none check if there's a transport route at all under the bridge

(svn r3905) -Fix: When returning the rail type under a bridge, check if there are rails at all

(svn r3904) Move GetBridgePiece() and GetBridgeType() to bridge_map.h and make the only place which still extracted that info diretly use the wrapper

(svn r3903) Fix a copy&pasto in last commit and remove a redundant comment (the line above already says what's going on)

(svn r3902) When drawing a bridge middle part get the bridge axis only once instead of again and again

(svn r3901) Remove the last user of FindEdgesOfBridge() by using functions with similar functionality

(svn r3900) When clearing a bridge determine the bridge direction and tile offset once instead of all over the place; also use UpdateSignalsOnSegment() instead of SetSignalsOnBothDir(), because this is sufficient

(svn r3899) Use wrapper functions to make more clear how deleting stuff under bridges works; also remove an unnecessary local variable