Raise ProgrammingError for nan and inf (#314)

* Raise ProgrammingError when inf or nan is passed
  Fixes #246
* Rename _mysql_exceptions -> _exceptions

MySQLdb/compat.py

@@ -5,8 +5,10 @@ if sys.version_info[0] == 2:
     unicode = unicode
     unichr = unichr
     long = long
+    StandardError = StandardError
 else:
     PY2 = False
     unicode = str
     unichr = chr
     long = int
+    StandardError = Exception