Done clean-up in prep stmt API functions:
1) Removed some checks that were performed only in debug version
were making debug version more tolerable to user errors than 
production (and thus caused problems for example masking some
bugs). 
2) Also removed some other checks to make prep stmt API 
consistent with the rest of C API (this also in line with 
general politics - make checks in only those places where 
errors are very common and hard to spot).


include/mysql.h:
  Removed CHECK_EXTRA_ARGUMENTS define since it is no longer used 
  anywhere.
libmysql/libmysql.c:
  Added check that will cause mysql_fetch() to bark then it is 
  used without calling mysql_execute() before.
  Removed checks that were performed only in debug version and
  caused problems since they were making debug version more 
  tolerable to user errors than production. Also removed some
  other checks to make prep stmt API consistent in this regard 
  with the rest of C API (this also in line with general politics -
  make checks in only those places where errors are very common 
  and hard to spot).
tests/client_test.c:
  Updated tests to reflect removal of some checks in prep stmt API.
  Removed lines that caused bug #2473 to pop up, should be added 
  as separate test with the fix for this bug.
  Added test for bug#2248 "mysql_fetch without prior mysql_execute 
  hangs"