Fix for CRM-12428

v3.3.beta1 - had label required (NOT NULL) for fresh installations, but optional (NULL) for upgrades [refer 3.3.bat1.mysql create table structure].

4.2.alpha1 - When upgrade passes through v4.2.alpha1 stage / script :
Eileen's patch would work cleanly for installations that upgraded to v3.3.x (gone though v3.3.beta1 script). 
Eileen's patch would still FAIL for v3.3.x fresh installations, as label would be a required field at DB level and following code fails at DB level:
CRM_Upgrade_Snapshot_V4p2_Price_BAO_FieldValue::create($options, $optionsIds); 

v4.2.3 - makes label column optional for both fresh installs and upgrades per CRM-11014

An appropriate solution would be to make label column optional at v4.2.alpha1 level itself in addition to Eileen's patch.