support setting the color of normal text

- message bodies
- system log
- inlined attachments

Not sure if I missed a spot
Merge #76: Accept UTF8 as UTF-8 and test encoding with fallback to UTF-8

Fixes #71.

Squashed commit of the following:

commit 9ce3664e296fb190473717bcd08e772184ff8242
Author: Gaute Hope <eg@gaute.vetsj.com>
Date:   Wed May 29 08:33:26 2013 +0200

    test encoding and fallback to utf-8

commit b17e917565e0a13671c0aaf08c22bfbf63ff5bb4
Author: Gaute Hope <eg@gaute.vetsj.com>
Date:   Wed May 29 00:12:16 2013 +0200

    accept UTF8 as UTF-8
Merge pull request #78 from mklinik/color-normal-text

support setting the color of normal text
Get rid of gettext

We actually only need the locale gem.
Switch xapian binding to xapian-ruby
Use ~> in gemspec correctly
Notify user to remove xapian-full-alaveteli
Use add_runtime_dependency in gemspec
Merge #83: Switch xapian binding to xapian-ruby
poll.rb: remove some ws bs
Source poll thread safety: lock source polling
move go_idle to ensure
change @polling to Mutex for thread safety
Merge #85: Check if GPG end marker exists

Picked up by @manizzle.

"lines.between() does not check if the end marker actually exists, but
later it is assumed the marker exists. This change introduces a check
for the end marker and doesn't decrypt messages in which the end marker
is missing. This is a fix for http://rubyforge.org/pipermail/sup-talk/2010-August/004209.html"

Source:
http://permalink.gmane.org/gmane.mail.sup.devel/641
Grammar :-)
Merge #84: Lock source poll: Thread safe polling
Replace Iconv with built-ins for Ruby >=1.9
patch RMail field parser to use UTF-8 regexps and fix_encoding before parsing field
more robust fix_encoding
Don't require iconv anymore