Merge pull request #970 from mditzel/master

Fix issue #969
Fix issue #969
Fix issue #971
Merge pull request #972 from mditzel/master

Fix issue #971
Change ToolsVersion to 4.0 for VS2010
Reference default locations for libsodium for VS2010
Merge pull request #973 from HughPowell/master

Change ToolsVersion to 4.0 for VS2010
Fixed mingw poll detection
Merge pull request #974 from xantares/master

Fixed mingw poll detection