Fix warnings raised by the compiler - #46

• When running the tests compile the code with warnings using the --enable-php-debugger-dev flag when configuring (this flag has been renamed from the old --enable-xdebug-dev name
• Fix existing warnings which had not been found because we had not been using this option, mainly removes unused functions and variables and makes sure that variable declaration is not mixed with code
• Apply two new warnings -Wstrict-prototypes and -Wold-style-definition and fix the issues found by them

This is probably better reviewed by looking at the individual commits

Note: I was not able to apply the -Wmissing-prototypes warning because our code uses several Zend macros which define functions without adding a prototype