Make targets phony so they always execute

Targets that do not create themselves should always be declared phony so
that they are never considered up to date.

http://www.gnu.org/software/make/manual/make.html#Phony-Targets

On case insensitive file systems, e.g. HFS+ on Mac OS X, make install is
always up to date because Make finds the INSTALL directory.
Merge pull request #11 from okorz001/phony-targets

Make targets phony so they always execute