add custom update targets, disable update from cmake externals_project
pool construction of update targets
correct typo
add missing file
Add a build custom target.
Fix dependeces between build-{ep} targets
Add an argument to EP_AddCustomTargets in order to checkout a specific tag, commit, or revision.
Fetch the 'url' defined by the externals before 'git checkout tag' when 'make update'.
 Add some lines to say to the user which command run after 'make update'.
Changed SVN update command
Removed TAG argument in the macro, as well as coloring
Added a git checkout master to handle going from tagged to untagged
Fixed typo
Merge pull request #32 from medInria/0000-custom-update-final

Adding update & build targets to SP