Give installed libraries execute permissions

All shared object libraries should have execute permissions. Using install will default the permissions to be like a normal file, which typically doesn't have execute permissions.
Merge pull request #40 from cottsay/master

Give installed libraries execute permissions
Update CHANGELOG.rst for 3.1.5-6
Merge pull request #42 from 130s/master

Update CHANGELOG.rst for 3.1.5-6
remove installed file if openhrp3_FOUND is not found
Merge pull request #45 from k-okada/fix_when_cache_removed

remove installed file if openhrp3_FOUND is not found
Update CHANGELOG.rst for 3.1.5-6
Merge remote-tracking branch 'origin/master' into fix_link_rotation