* testsuite/Makefile.in: Use %-rules for building the -test

executables, in addition to the suffix rules. Hopefully, this
should make all of GNU make, BSD make and Solaris make happy.
Use $(EXEEXT) and $(OBJEXT) more consistently.

Rev: src/nettle/examples/Makefile.in:1.12
Rev: src/nettle/testsuite/Makefile.in:1.19