Add null constraint for issuenum column to jiraissue table

                  Table "public.jiraissue"
        Column        |           Type           | Modifiers
----------------------+--------------------------+-----------
 id                   | numeric(18,0)            | not null
 pkey                 | character varying(255)   |
 issuenum             | numeric(18,0)            |
 project              | numeric(18,0)            |
...
Indexes:
    "pk_jiraissue" PRIMARY KEY, btree (id)
    "issue_assignee" btree (assignee)
    "issue_created" btree (created)
    "issue_duedate" btree (duedate)
    "issue_proj_num" btree (issuenum, project)
    "issue_proj_status" btree (project, issuestatus)
    "issue_reporter" btree (reporter)
    "issue_resolutiondate" btree (resolutiondate)
    "issue_updated" btree (updated)
    "issue_votes" btree (votes)
    "issue_watches" btree (watches)
    "issue_workflow" btree (workflow_id)