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
gridsort+resort: bugfixes
p2nfft: add resort support
sl: bugfix
Merge branch 'master' into update
fmm: add resort support
Merge pull request #10 from mh0fm4/master

Add (optional) resort support in p2nfft and fmm (i.e., keep sorted particle order and use it in the next time step)
fix several warnings
Merge branch 'master' of github.com:scafacos/scafacos