Add a warning for unbound constraints in the validating loader

Closes #2165
Added a new FAQ entry about unbound version constraints
Merge remote-tracking branch 'stof/doc_unbound'
Adjustments to unbound constraint docs
Merge remote-tracking branch 'origin/master'
Add dev-master example
Merge remote-tracking branch 'stof/validate_unbound_constraints'
Only check in require and for non-platform packages, add flag to make this warning optional, refs #2320
Correctly add decision reason to transaction
use HHVM_VERSION

this one is better (they are the same)
When requiring a package remove it from require-dev and vice versa
Merge pull request #2892 from ptarjan/patch-1

use HHVM_VERSION
Add an --update-no-dev option to the require command
Merge pull request #2893 from naderman/require-delete-duplicate

When requiring a package remove it from require-dev and vice versa
Merge pull request #2894 from naderman/update-no-dev

Add an --update-no-dev option to the require command