Don't bulk add all /usr folders for includes or libs.

This causes problems for some systems with Qt5 and Qt4 installed (like Fedora 20).

QGCExternalLibs.pri

-#
-# [REQUIRED] Tell the Linux build to look in a few additional places for libs
-#
-LinuxBuild {
-	INCLUDEPATH += \
-        /usr/include \
-        /usr/local/include
-
-	LIBS += \
-		-L/usr/lib
-
-    linux-g++-64 {
-        LIBS += \
-            -L/usr/local/lib64 \
-            -L/usr/lib64
-	}
-}
-
 #
 # [REQUIRED] Add support for <inttypes.h> to Windows.
 #