Use OPENNI2_INCLUDE64 environment variable.
(Set on windows with install from http://structure.io/openni).
updated linux installation documentation
Merge remote-tracking branch 'upstream/master' into daniel
Merge pull request #3422 from avdmitry:install_doc_update
Merge pull request #3424 from dsjolie:daniel
Doxygen config changed

- disabled tree
- enabled enum listing
- added imgproc reference to main page
Documenting imgproc module: filters subgroup
Documenting imgproc module: transformations subgroup
Enabled existing BiB cite support
Documenting imgproc module: miscellaneous subgroup
Documenting imgproc module: other subgroups
Documenting imgproc module: C-interface
Documenting imgproc module: more fixes