Correct a couple of minor bsdgrep(1) assumptions that are valid for line processing
but not future chunk-based processing.
Rename MAX_LINE_MATCHES to MAX_MATCHES; the name is kind of misleading to begin with, since it's
actually the maximum number of matches we'll process in one pass at the line. There is currently
a bug in that we're actually limiting line matches to MAX_LINE_MATCHES, which is wrong and to be
corrected in D10577.
Additionally, we set REG_NOTBOL if st > 0, but that's only correct if st is an index into a line-based
buffer. Correct this one simply by checking also that the character preceding is not EOL to hold up when
we're looking beyond a single line.
These are some low-hanging fruit and should clean up the rest of procline. The name will be addressed
when its input is actually no longer expected to be a single line, but the additional assumptions were cleared
with rS317703 lifting line/context printing out into procfile.
Future work will be to remove line-based assumptions from procfile by pulling in chunks and processing the
matches produced by procline there to determine line numbers, etc. as needed.