Add two tools: mkdoubledirs and gensamehash

mkdoubledirs creates pairs of directories a/a, b/b, c/c etc. This is to
test file lookup code: there must be a directory named blah only if the
current directory is named blah too.

gensamehash generates file names with the same XFS hash to test the
code that resolves collisions. In principle, can be updated for other
hashes: ext*, exfat, etc.

.gitignore

@@ -8,10 +8,12 @@ umka_fuse
 umka_os
 umka_ping
 umka_gen_devices_dat
-mkdirrange
-mkfilepattern
-lfbviewx
-randdir
+tools/mkdirrange
+tools/mkdoubledirs
+tools/gensamehash
+tools/mkfilepattern
+tools/lfbviewx
+tools/randdir
 *.img
 *.img.xz
 *.img.gz