add a basic textarea cf test (cf type Text) for issues#30378
Rewite HasEntry logic that determines if new custom field value matches existing value.

_ProcessObjectCustomFieldUpdates calls AddCustomFieldValue with a 'Value'
parameter unconditionally instead of deciding if it should pass 'LargeContent'
instead when the content is long enough, so HasEntry always returns false
for LargeContent data.

This commit makes HasEntry check $value against LargeContent instead of
expecting $large_content to be passed.

fixes issues#30378
Merge branch '4.2/hasentry-for-largecontent' into 4.2-trunk