added more reserved words to real_escape_string function

Use of real_escape_string function plus some reserved words
substitution. In the original function, reserved words like SELECT,
INSERT, and many others are not validated so the default
real_escape_string is not good enough to void injections in Mysqli
querys. I just added a validation that take out some reserved words and
after we use the default real_escape_string function. The result is a
Mysql sentence cleaned and without any risk of code injection.