Generate list of .d and .testdep files from UNIT_TEST_BINARIES
Put tr, sed and grep in variables in makefile
Add explicit rule to make mock .o files and accept both full path and filename only in mock generation rule.
Insert newline after mock generation output
Informative message when making .testdep. Silence messy command.
Make testdep rule still depend on DEPS_DIR but not be triggered by the directory being updated.

The directory is updated each time a file in it is changed. Make seems to have been able to split this circle before, but it might have resulted in the testdep being built too often or when not necessary.