Fix more compiler warnings when compiling single file with -Wall

Fixes:
  * ‘phalcon_less_equal_long’ declared ‘static’ but never defined — implemented the function
  * ‘phalcon_try_execute’ declared ‘static’ but never defined — commented out the definition
  * ‘phalcon_restore_symbol_table’ declared ‘static’ but never defined — commented out the definition
  * 'phalcon_call_user_function_ex', 'phalcon_call_function', 'phalcon_lookup_class_ex' and 'phalcon_lookup_class' declared ‘static’ but never defined — implementation is provided only for PHP <= 5.3.9, therefore I moved their definitions under `#if PHP_VERSION_ID <= 50309`
  * 'phalcon_alt_call_user_method_ex' declared 'static' but never defined — commented out their definitions.