regexec.c: Simplify a short code section

Two "if"s can be combined, leading to one fewer (unoptimized) tests
regcomp.c: Remove unnecessary test

The 'while' makes the 'if' unnecessary here.
regcomp.h: Fix comment that said the opposite of the truth

Too many negations led to this.
regcomp.h: Use unsigned 1 in left shift

This prevents a signed result if this macro ever gets used in a U8.
The ANYOF_BITMAP_TEST macro must now be cast or it would generate warnings
when compiled with -DPERL_BOOL_AS_CHAR
regcomp.h: Remove some no-longer used #defines

This is an internal header, so can change names within it.
Rename some internal regex #defines

These are renamed to be more clear as to their actual meanings.  I know
other people have been confused by their former names.

Some of the name changes will become more important as future commits
will allow the bitmap in a bracketed character class to be a different
size.
regcomp.c: Swap if/else clauses

This makes it slightly easier to understand as there is no explicit
complement, but is mostly for a future commit.
Fix -Dr output to work for larger ANYOF node size

This generalizes the code for -Dr output to work to dump the contents of
ANYOF nodes (bracketed character classes) which have bitmaps for more
than code points 0-255.
Allow for changing size of bracketed regex char class

This commit allows Perl to be compiled with a bitmap size that is larger
than 256.  This bitmap is used to directly look up whether a character
matches or not, without having to do a binary search or hash lookup.  It
might improve the performance for some installations that have a lot of
use of scripts that are above the Latin1 range.
regcomp.h: Comment nits