add VPATH support to Makefile
add -g to CFLAGS; understand EXTRA_CFLAGS
add VPATH support to tests/Makefile

* scripts use $CVS_FAST_EXPORT to find program
* diff -a, so can always see diffs
spelling, typos
remove checks for impossible NULLs
preserve errno
add more gcc hints for optimisation
add xmemalign
make atom() thread-safe
add bloom filter framework
fix segv on empty input
fix 64-bit compile warning
use bloom filter
pack memory a little better
avoid restarting iterator during parent linking
sort directories first to improve memory packing
reduce size of struct fileop, using atoms

* factored out common path_deep_compare() function so that
  export function works with read-only strings,
* improved performance of export_filename
optimizing the file compare
don't keep patches in memory

* new cvs_text structure (filename, offset, length)
* patches are read during generate
* avoid malloc calls in scanner for short rcs texts
avoid fopens by using an LRU mmap cache

* also changed a constant pointer to a define