Adding include element into the top-level element
Adding include element into the top-level element

The documentation of the XML file format contains DTD which contains
definition of all allowed elements and attributes. The "include" element
is defined but it's not referenced from the top-level "manifest"
element.

This patch is adding the "include" element into the list of elements of
the top-level "manifest" element.

Change-Id: I33beb8ef2846bbf42ffd42e6ae6888828566d604

TheQtCompany/git-repo,chenzilin/git-repo,nuclearmistake/repo,lewixliu/git-repo,couchbasedeps/git-repo,GerritCodeReview/git-repo,lipro-yocto/git-repo,TheQtCompany/git-repo,lewixliu/git-repo,mer-tools/git-repo,wavecomp/git-repo,mer-tools/git-repo,chenzilin/git-repo,codetutil/git-repo,aosp-mirror/tools_repo,lipro-yocto/git-repo,codetutil/git-repo,gabbayo/git-repo,GerritCodeReview/git-repo,couchbasedeps/git-repo,nuclearmistake/repo,gabbayo/git-repo,wavecomp/git-repo,aosp-mirror/tools_repo