debug.php: Add a pip_debugging() function

Issue #103.
debug.php: Fix line length

Issue #103.
configure: Add --enable-debug option

Issue #103.
htaccess: Set DEBUG variable based on configure arg

Debugging is now controller with the --{enable,disable}-debug configure
option.

Issue #103.
configure: Print whether we're building a debug site

Issue #103.
debug.php: Add pip_get_debug_var() function

Issue #103.