Fix exact tag match check to set the release.version property

With this commit, the `init-version` target should not append a `-DEV`
suffix is the current commit is exactly matching a tag.
Add comment explaining why 'instanceof' is checked
Redo POM version number hardcoding

Using variable version numbers is very much unsupported in Maven 3.
Probably we'll need to write a script for release jobs to use that
manually replaces the hardcoded version numbers.
Merge remote-tracking branch 'origin/develop' into maven-build-numbers
Force top-level Maven build to run as part of cppwrap
Merge pull request #681 from sbesson/downloads_page

Bio-Formats downloads page
Merge pull request #682 from sbesson/release_version_fix

Release version fix
merge develop -D org -I include -E exclude: PR 528 (Tile performance improvements for VMS and NDPI)
merge develop -D org -I include -E exclude: PR 635 (Use jgit-buildnumber to set version information in Maven)
merge develop -D org -I include -E exclude: PR 640 (cpp: Add initial C++ implementation)
merge develop -D org -I include -E exclude: PR 643 (Data test updates)
merge develop -D org -I include -E exclude: PR 644 (Add support for writing ModuloAlong* annotations)
merge develop -D org -I include -E exclude: PR 646 (Save current revision number in memo file)
merge develop -D org -I include -E exclude: PR 647 (Make JDK 1.6 the minimum supported version)
merge develop -D org -I include -E exclude: PR 679 (Multi-plane flex file with factor and no compression only reads first pl...)