[MRRESOURCES-91] Avoid overwrite of the destination file if the produced contents is the same

maven-remote-resource-plugin is used in Apache pom to add DEPENDENCIES, and the resulting file is overwritten on each build.
It leads to jar being rebuild, etc leading to longer compilation times.

Patch by Vladimir Sitnikov <sitnikov.vladimir@gmail.com>

This closes #40

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1646543 13f79535-47bb-0310-9956-ffa450edef68