Reusing library: model change not respected

[kilian]

When rerunning a sindarin file, the matrix element code should be regenerated if just the model has changed. This is currently not the case (see libraries_3): the model should be included in the MD5 sum process components, not just processes. Even better: the model's MD5 sum.

[kilian]

Actually, three bugs and much harder than expected: the model info was not taken into account, process components didn't get their MD5 sums in time, and Make had to be convinced to really remake the sources when being told. Fixed in r4591.