fetchsingular: fix wget support
fetchsingular: verify MD5 of tarball
fetchsingular: change to download Singular 4.0.0.p4
Add {configure,make}singular.debug scripts

Use these to build singular with debug flags enabled. Both install into
singular/dst to make it easy to switch between the two: Just run
  ./makesingular && make
or
  ./makesingular.debug && make
to (relatively) quickly switch between normal and debug mode. (To make
it even faster, remove the "make check" from your copy of makesingular).
libsing.h: #include assert.h
Remove mmInit

Neither Singular 4.0.0.p4 nor Singular.git need it anymore