This should fix at least some instances of the "undefined
reference to `LLnc_recover'" error that happens in some
builds (https://github.com/davidgiven/ack/issues/218).
The bug was that genname( ) used a static `namebuf' buffer
and did not properly check for overflow when writing into
it. The result was that the `non_corr' variable was
sometimes overwritten with a non-zero value when it should
be zero, causing bogus results later.
This proposed patch makes genname( ) dynamically allocate
and resize a buffer for holding a target file name.
I also take this chance to fix a typo in correct_prefix().
9c7ce04cec