regcomp.c: Add comments; align ternary operator for clarity
regcomp.c: Stop potential leaks

These two ref counts were not at the same level as their corresponding
dec.
Add warnings for "\08", /\017/

This was discussed in thread
http://perl.markmail.org/thread/avtzvtpzemvg2ki2
but I never got around to this portion of the consensus, until now.