PIR/PASM/PBC files without extensions

[Allison Randal]

I'm about to add a deprecation notice for a feature I thought I rejected 
a couple of years ago. Quick check first to see if anyone's using it, or 
planning to use it.

The feature is the ability to load_bytecode without a file extension, 
and have it try '.pbc', '.pasm', and '.pir' to see if such a file exists.

The alternative I propose to implement is to always require a file 
extension, but fallback and check an alternate file extension if the 
first one isn't found. So, if your file extension is:

.pir -> if not found, check for a .pbc file

.pasm -> if not found, check for a .pbc file

.pbc -> if not found, check for a .pir file, then for a .pasm file

This allows developers to choose whether they prefer source or compiled 
form, and optimizes for the common case (.pir and .pbc). It also fits 
better with current usage, as PASM is no longer a half-way stage for 
PIR, but a separate language.

Allison