Optimize some functions unnecessarily relying on BEGIN EXCEPTION blocs

[pedrogit]

As stated in the plpgsql documentation: "A block containing an EXCEPTION clause is significantly more expensive to enter and exit than a block without one. Therefore, don't use EXCEPTION without need."

• TT_IsInt() - Can be replace by a regular expression
• TT_IsCastableTo()
• TT_IsNumeric()
• TT_IsBoolean()
• TT_IsStringList()