Bug#939663: freefem++: B-D on cruft packages

[Esa Peuha]

Source: freefem++
Version: 3.61.1+dfsg1-4
Severity: serious

Currently freefem++ build-depends on libpetsc-real3.10-dev and
libpetsc-complex3.10-dev which are no longer built from source.
Please update these build-dependencies.