It is now set to 0 when progs are loaded and every time
PR_ExecuteProgram() returns. This takes care of the default case, but
when setting parameters, pr_argc needs to be set correctly in case a
vararg function is called.
Use the resource map code for handle management (much safer).
Add support for the enter callback (function or method).
Unfortunately, it still doesn't work due to poor design of the inputline
user data.
