bugfix: codegen.c makes function call using func_name, but func_alias should be used
add opencl_mathlib.h for more compatible behavior with PostgreSQL
bugfix: makes some arithmetrics functions more compatible with PgSQL

according to the research at #5, codegen.c was reworked.
arithmetrics operators (+-*/) on int/float were moved to pre-declared
functions to handler overflow/zero-division check correctly.
fixbug: incorrect catalog of codegen.c definition on cast functions
Merge branch 'master' of ../pg_strom
removed a garbage