Merge pull request #1 from scafacos/master

p3m: remove execute permisson on source file
Merge remote-tracking branch 'upstream/master'
Merge branch 'master' of github.com:scafacos/scafacos
sl: update sorting library
p2nfft: fix check and integration of math and GSL libraries
Merge branch 'master' of github.com:scafacos/scafacos