Created attachment 1289894 [details]
accept underscore in external tracker type

Attempting to edit an external tracker with type SFDC_QA gives the error
  "SFDC_QA" is not a valid external tracker type. 
with the title "Invalid Type Supplied".

This appears to come from extensions/ExternalBugs/lib/Type.pm:309
    $type =~ /^([A-Z][A-Za-z0-9]+)$/i
        or ThrowUserError('ext_bz_unsafe_chars', { type => $type });
not accepting underscore