optionally specify method compilation environment in packageNameToPlatformPropertiesMap

[dalehenrich]

Something like the following would cause all methods in the PharoMods-Core package would compiled in method environment 2:

	#conditionalPackageMapSpecs : {
		'gemstone' : {
			'SystemUser' : {
				#packageNameToPlatformPropertiesMap : {
					'PharoMods-Core' : { 
						'symbolDictName' : 'Globals' },
						'methodEnv' : 2 }
					}
				}
			}
		}
	}

This is needed to support the PharoGs project