xbhconfig.h->xbh_config.h

also updated lwipopts.h for latest version of lwip in git
Updated lwip
Reorganize headers and includes
Fixed GDB step/post-step hooks

Interrupts would be reenabled by tasks if they weren't disabled first.
Moved priority definitions

Doing this since any changes in lwipopts or included files triggers a
rebuild of lwip
Implemented xbh git revision command

Also added ntoa as a dependency in utils.[ch]

Reorganized some makefile defines