Xdebug remote debugging compatibility and bug fixes

This diff finishes the last two remote debugging commmands property_get
and property_set, fixes remote debugging bugs, and adds compatibility fixes
to ensure remote debugging works with phpstorm, komodo, netbeans, and vim.

Specific changes:
* Implemented property_set and property_value
* Updated tests broken with the below changes
* General cleanup

Compatibility:
* Added $GLOBALS variable to superglobal list
* Contexts should start at 0 for komodo to be happy
* Replaced calls to xdebug_get_php_symbol with an eval. There were bugs
  with xdebug_get_php_symbol and I discovered phpstorm, komodo,
  netbeans, and the vim plugin always just send an expression.

Bug Fixes:
* xdebug.idekey ini setting was incorrectly named xdebug.ide_key
* When outputting arrays to xml the page was always set to 0
* The variable exporter needed state to be reset in between exports
* When adding breakpoint info to xml nodes data needed to be duplicated
  as the breakpoint could be deleted before the node was sent
* names in property_get were assumed to be base64 encoded
* stack_get was being used differently than expected. E.g. level 0 is
  intended to be the current location. Also, there were bugs in
  determine line location.