Merge branch 'v2.5' of https://github.com/plumed/plumed2 into v2.5

.travis/install.xdrfile

@@ -6,12 +6,15 @@ set -x
 cd "$(mktemp -dt plumed.XXXXXX)"
 
 echo "installing xdrfile library"
-wget ftp://ftp.gromacs.org/pub/contrib/xdrfile-1.1.4.tar.gz
+# wget ftp://ftp.gromacs.org/pub/contrib/xdrfile-1.1.4.tar.gz
 # xdrfile was removed from gromacs ftp
 # as a workaround I added a copy to people.sissa.it/~bussi/plumed
 # this complies with its license
 # wget people.sissa.it/~bussi/plumed/xdrfile-1.1.4.tar.gz
 
+# better to download from github, that should be even more reliable:
+wget https://github.com/plumed/other_packages/blob/master/xdrfile-1.1.4.tar.gz
+
 tar xzf xdrfile-1.1.4.tar.gz
 
 cd xdrfile-1.1.4