Adds support for ILMerge's /allowMultiple switch.
Adds support for ILMerge's /allowMultiple switch.

stimpy77/msbuildtasks,smallkid/msbuildtasks,AArnott/msbuildtasks,jricke/msbuildtasks,arekbee/msbuildtasks,loresoft/msbuildtasks,wrozmiarek/msbuildtasks