Add protocol input option
Merge branch 'master' into xml-parser

manually merged src/tracer.c
Change unspecified new_id's signature from sun to N

to make it more convenient
Add XML protocol parser, remove hardcoded protocol

This huge commit adds in the XML protocol parser and support routines,
making the interpret mode pratical. Also the original hard-coded
protocol are removed, eliminating the problems described in previous
commit message.

Note that we're migrating from wl_* structures about interfaces,
messages and so on to our own tracer_* structures to facilitate
potential improvements.
Merge branch 'xml-parser'