Patch tdb to compile with the new Makefile and gcc 4.6.3

Hello, I see that recently you updated the Makefile to abort when
warnings are encountered. As a result, the following happens when
I try to build tdb (my compiler is gcc 4.6.3):

tdb/tdb.c: In function ‘tdb_shell’:
tdb/tdb.c:38:8: error: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Werror=unused-result]
cc1: all warnings being treated as errors
make: *** [tdb/tdb.o] Error 1

The attached patch fixes the issue.

By the way, are you considering adding indexed/indirect addressing
to tinyvm ? It would allow local (stack) variables in routines and pointers,
which would make tinyvm really complete.