up #387 : fix explicit parallelism

Conflicts:
	doc/manual/laplacian/CMakeLists.txt
	feel/feelalg/backendeigen.hpp
	feel/feelalg/matrixsparse.hpp

(cherry picked from commit 12e37be91e7a29baaaaea2d9bd19b2bb11175a44)

Conflicts:
	feel/feelalg/matrixeigendense.hpp
	feel/options.cpp
Merge branch 'merging-with-explicit' of https://github.com/feelpp/feelpp into merging-with-explicit