Turn off warnings as errors as default

Also changed WarningsAsErrorsOff to WarningsAsErrorsOn to be used by
TeamCity builds.

qgroundcontrol.pro

@@ -130,34 +130,16 @@ WindowsBuild {
 }
 
 #
-# We treat all warnings as errors which must be fixed before pull requests are approved. If you run into a problem 
-# you can't fix you can always use local pragmas to work around the warning. This should be used sparingly and only 
-# in cases where the problem absolultey can't be fixed.
+# By default warnings as errors are turned off. Even so, in order for a pull request 
+# to be accepted you must compile cleanly with warnings as errors turned on the default 
+# set of OS builds. See http://www.qgroundcontrol.org/dev/contribute for more details. 
+# You can use the WarningsAsErrorsOn CONFIG switch to turn warnings as errors on for your 
+# own builds.
 #
-# If you run into problems in code which is not yours, please lend a hand and fix the issues. If you don't have time
-# for that post an Issue with your OS and compiler information as well as the pertinent output from the build log. If it's
-# a problem that will take longer to fix, we will temporarily turn off warnings as errors for that specific config until
-# the Issue is taken care of. Once that is completed we will turn warnings as errors back in for the config. You can use
-# CONFIG+=WarningsAsErrorsOff in your private builds for a quick local override.
-#
-# Please report any problems you run into with warnings as errors so we can gather information on its effectiveness as well
-# as its annoyance level.
-#
-
-# Note: -Werror is currently not turned on for Linux due to unfixed problems with release builds. See Issue 535. This will 
-# be removed once the Issue is taken care of.
-# Note: -Werror is also not turned on for Mac because Qt Core throws unused variable warnings for Mac from multiple header files.
-
-MacBuild | LinuxBuild {
-    CONFIG += WarningsAsErrorsOff
-}
 
 MacBuild | LinuxBuild {
 	QMAKE_CXXFLAGS_WARN_ON += -Wall
-}
-
-MacBuild | LinuxBuild {
-    !WarningsAsErrorsOff {
+    WarningsAsErrorsOn {
         QMAKE_CXXFLAGS_WARN_ON += -Werror
     }
 }
@@ -166,10 +148,9 @@ WindowsBuild {
 	QMAKE_CXXFLAGS_WARN_ON += /W3 \
         /wd4996 \   # silence warnings about deprecated strcpy and whatnot
         /wd4290     # ignore exception specifications
-}
-
-WindowsBuild : !WarningsAsErrorsOff {
-	QMAKE_CXXFLAGS_WARN_ON += /WX
+    WarningsAsErrorsOn {
+        QMAKE_CXXFLAGS_WARN_ON += /WX
+    }
 }
 
 #