Symlink libreaddir-rand.so into tests directory

This means it can be LD_PRELOADed during build-time testing.

Signed-off-by: Simon McVittie <smcv@debian.org>

Closes: #232
Approved by: cgwalters

.gitignore

@@ -70,6 +70,7 @@ _build
 /test-remote-add.test
 /test-setuid.test
 /test-xattrs.test
+/tests/libreaddir-rand.so
 test-varint
 test*.test
 *.trs