* tools/tiffdump.c: Fix double-free bug.
Update the valgrind memcheck recipe for the test suite.
* tools/tiff2pdf.c (t2p_read_tiff_init): TIFFTAG_TRANSFERFUNCTION
tag can return one channel, with the other two channels set to
NULL.  The tiff2pdf code was expecting that other two channels
were duplicate pointers in the case where there is only one
channel.  Detect this condition in order to avoid a crash, and
presumably perform correctly with just one channel.
tools/thumbnail.c, tools/tiffcrop.c: fix heap read over-run found with Valgrind and Address Sanitizer on test suite
* tools/tiff2pdf.c: Assure that memory size calculations for
_TIFFmalloc() do not overflow the range of tmsize_t.