Support logical arrays in blob columns without data type conversion

Based on the resolution of mym issue 3 and thus requires mym version 2.6.8+
fixed dj.GeneralRelvar/restrict that was broken in 3dbeca0. Also, removed one query to information schema with a regular query as part of fixing issue #22.
All restrictions now invoke dj.GeneralRelvar/restrict rather than append restrictions directly.
incremented version to 2.6.9
Merge branch 'future'
incremented version to 2.6.9
Added destructor to dj.Connection to close the mym connection when objects are destroyed. Fixed a bug in dj.struct/tabulate that was affecting 1D tabulation.
fixed dangerous bug introduced in c7d4a0c and affecting releases 2.6.8 and 2.6.9.  Deletes were not restricted by the specified restrictors.
incremented version to 2.6.10
Merge branch 'future'
made dj.BaseRelvar/del more efficient by not deleting from tables when nothing is to be deleted.