Log Message:
Update to 1.41.  Selected changes:
* add options -l, -r and -t.  add to -f option
* improve I/O on Linux using fgetc_locked().
* improve searching of long sorted lists using tsearch()
* change order of merging and prefix-stripping so stripping all prefixes,
  e.g., with -p9, will be sorted as expected
* correct a reference to freed memory after merging found with valgrind.
* fix a different case for data beginning with "--" which was treated as
  a header line.
* Fix allocation problems.  Open files in binary mode for reading.
  Getopt returns -1, not necessarily EOF.  Add const where useful.  Use
  NO_IDENT where necessary.  malloc() comes from <stdlib.h> in standard
  systems
* minor fix for resync of unified diffs checks for range (line beginning
  with '@' without header lines (successive lines beginning with "---"
  and "+++")