BP_VERSION / BP_DB_VERSION constants are empty

[r-a-y]

Because the BuddyPress::constants() method is called before BuddyPress::setup_globals() (where the version variables are defined), it's impossible to set the BP_VERSION and BP_DB_VERSION constants.

In the attached patch, I have moved $version and $db_version out of setup_globals() and into main class properties so the constants will still work and will not break any existing plugins relying on them.

[johnjamesjacoby]

I'd rather we reverse this approach for non-bootstrap constants; have a legacy constants method/function to separate non-essential constants (that aren't used anywhere by BuddyPress core anymore) apart from the overloading-constants (like _SLUG).

(Edit: huge run-on sentence; add punctuation.)

[ddean]

Here's an alternate patch in line with JJJ's suggestion. I didn't touch the search slug, and
all other constants besides BP_VERSION and BP_DB_VERSION are used in setup_globals(), so the legacy constants method ended up pretty bare.

[dcavins]

I noticed this problem because BP Template Pack started loading the wrong css file under BP 1.7 (it selects which css file to include based on BP being over or under 1.3). This patch restored expected behavior (bp_get_version returns the same version as BP_VERSION).

[johnjamesjacoby]

(In [6590]) Introduce legacy_constants() method, to handle the setting of old BuddyPress constants that some plugins might still look for. Props ddean. Fixes #4550.