bug#17640: grep with -m reads the entire input

[Marc Aldorasi]

With grep 2.18, the -m option would cause grep to stop reading input
after printing the requested number of matching lines.  With version
2.19, grep reads the entire input before exiting.  Interestingly, grep
does not read the entire input if the -c or -C0 options are added in
addition to -m, and also when using -l or -q instead of -m.  I believe
this is caused by commit 5122195.