* Add new macros with variable number of arguments.
- in xbt/log.h: XBT_DEBUG, XBT_VERB, XBT_INFO, etc.
- in xbt/cunit.h: xbt_test_{add,fail,assert,log}
+ - in xbt/ex.h: THROWF and RETHROWF.
Define XBT_USE_DEPRECATED if you want to use the old numbered macros like
INFO1, INFO2, etc.
* Change xbt_die() to accept a format string with arguments, just like printf.