thread_view_mode: Kill a message (and next, prev etc..)
sup-sync: error msg on :update
Merge #300: sup-tweak-labels sync back unless specified otherwise

Squashed commit of the following:

commit ebfb3335070bba8e27551dcc4c232a4de2e98044
Author: Wael M. Nasreddine <wael.nasreddine@gmail.com>
Date:   Wed Apr 30 22:26:10 2014 -0700

    sup-tweak-labels: add a newline before the begin

commit f1d51d3961b0864c5f05f7b728cf5dd722a967eb
Author: Wael M. Nasreddine <wael.nasreddine@gmail.com>
Date:   Wed Apr 30 22:22:23 2014 -0700

    sup-tweak-labels: sync_back (honor the settings global and source) and provide an override

commit c43319a5fdfb725455beda51b7ec08799ecdda89
Author: Wael M. Nasreddine <wael.nasreddine@gmail.com>
Date:   Tue Apr 29 15:54:01 2014 -0700

    sup-tweak-labels: sync back if specified
sup.gemspec: Standarise the Gemspec
fix travis. The rake task to build a gem is now 'rake build'
Merge #303: Update gemspec and rakefile to use bundler
travis: drop 2.1.0 testing
Merge #301: thread_view_mode: Kill a message (and next, prev etc..)
Merge branch 'develop' into maildir-root

Conflicts:
	bin/sup-sync
history: bundler and threadkilling
Merge branch 'develop' into maildir-root
prepare for 0.18.0
add check-attachment hook
hitory, rel-notes: check-attachment
Display times in 24h format if configured so
readme: new mailing list: supmua@googlegroups.com
gem: new mailing list
readme: missing )
Merge #315: Display times in 24h format if configured so
prepare for 0.19.0