* Makefile.in: Don't use -include, as it's GNU make specific.

Added rule to create empty dependency files if they are missing.
* examples/Makefile.in, tools/Makefile.in, testsuite/Makefile.in:
Likewise.

Rev: src/nettle/ChangeLog:1.297
Rev: src/nettle/Makefile.in:1.9
Rev: src/nettle/examples/Makefile.in:1.6
Rev: src/nettle/testsuite/Makefile.in:1.6
Rev: src/nettle/tools/Makefile.in:1.7