Add a pair of tests for .zip extension check

TorrentZip should consider any file given explicitly as command line
argument, regardless of extension and type. On the other hand, when
processing a directory, only regular files with a .zip extension (case
insensitive) and subdirectories should be considered.

Add tests to check that files with different extensions are processed
or ignored as expected. We can't test with symlinks, sockets, or fifos
since nihtest doesn't support their creation in the sandbox.

regress/direct.test

@@ -0,0 +1,11 @@
+description torrentzip a file without .zip extension
+return 0
+arguments -l small.bin
+file small.bin small.zip small.tzip
+stdout
+Rezipping - small.bin
+--------------------------------------------------
+Adding - test.txt (31 bytes)...Done
+--------------------------------------------------
+Rezipped 1 compressed file totaling 31 bytes.
+end-of-inline-data

regress/recurse.test

@@ -0,0 +1,19 @@
+description find all zip files in a directory
+return 0
+arguments -l dir
+file dir/CaSe.ZiP small.zip small.tzip
+file dir/p small.zip
+file dir/skip.bin small.zip
+file dir/sub/small.zip small.zip small.tzip
+stdout
+Rezipping - dir/CaSe.ZiP
+--------------------------------------------------
+Adding - test.txt (31 bytes)...Done
+--------------------------------------------------
+Rezipped 1 compressed file totaling 31 bytes.
+Rezipping - dir/sub/small.zip
+--------------------------------------------------
+Adding - test.txt (31 bytes)...Done
+--------------------------------------------------
+Rezipped 1 compressed file totaling 31 bytes.
+end-of-inline-data