e-proxy: Eliminate use of undefined C behaviour

As much as this works fine in practice (because the function returns an
error, so mask->s_addr should never be used), we should avoid undefined
behaviour. Apparently it kills kittens.

Coverity issue: #1214484

https://bugzilla.gnome.org/show_bug.cgi?id=730379
secret-monitor: Remove duplicate assignment

Coverity issue: #1214503

https://bugzilla.gnome.org/show_bug.cgi?id=730371
addressbook: Fix some potential NULL pointer dereferences with SQL

The PreflightContext.constraints field may be NULL, especially when
calling query_preflight() with a newly-initialised context from
PREFLIGHT_CONTEXT_INIT.

Coverity issues: #1214492, #1214493

https://bugzilla.gnome.org/show_bug.cgi?id=730373
camel: Print a warning on failing to save migrated maildir version

Rather than ignoring potential failure completely.

Coverity issue: #1214488

https://bugzilla.gnome.org/show_bug.cgi?id=730375
camel: Avoid an unlikely division by zero on a race condition

This is a subtle and really unlikely TOCTTOU race which Coverity found.
Fix the potential division by zero which results from it.

Coverity issue: #1061271

https://bugzilla.gnome.org/show_bug.cgi?id=730376
addressbook: Add bounds checking to a summary file function

There was not a bug here, as the len parameter always came from a
guint16, so no overflow was possible. However, a bounds check is always
a good idea and makes the code more robust in the face of future
changes.

Coverity issue: #1061517

https://bugzilla.gnome.org/show_bug.cgi?id=730381