* mu4e/org-mu4e.el (org-mu4e-store-link): Add capture template keywords

For other email links (e.g., wl, mh, gnus), a number of keywords are
defined in org capture templates.  This makes these keywords available
for use in captures from mu4e.

http://orgmode.org/manual/Template-expansion.html

Inspiration from Roelof Burger
https://groups.google.com/d/msg/mu-discuss/4sffZofVKAY/aVTdVYoVyiUJ
mu: Test splicing child containers when there is only one thread

This test reproduces a regression introduced by commit 97101f1f82ba
("mu: Prune empty container when an only child gets promoted to the
root set").

When the results of a mu-find query contain only a one thread:

$ mu find --threads --fields 'd s' ''
Sat 09 Aug 2014 07:00:00 PM CEST [mu4e] Test Message
  `-> Sat 09 Aug 2014 08:30:00 PM CEST Re: [mu4e] Test Message

... and we narrow down the query in such a way that the root message
gets excluded, then a crash occurs:

$ mu find --threads --fields 'd s' '' date:2014-08-09/20:00..2014-08-09/21:00
**
ERROR:mu-container.c:117:mu_container_append_siblings: assertion failed: (c)
Aborted (core dumped)

Reported-by: Josiah Schwab <jschwab@gmail.com>
mu: Prune empty containers from the root set after splicing their children

When the root set contains only one empty container with one child
first promote the child container to the root set and only then
remove the empty parent container so that the root set never goes
empty.

Also make mu_container_splice_children() do only one thing, that is
promote one container's children to be another container's siblings.
The resultant childless container is no longer removed by this
function.

Fixes #460.
mu: Make mu_container_splice_grandchildren() do only one thing

Don't kill the resultant childless container when promoting its
children. This unifies the behavior of mu_container_splice_*()
functions.
Merge pull request #463 from jsitnicki/thread-sort-fixes

Remove empty container after promoting its children to siblings
Merge remote-tracking branch 'upstream/master'
Guard against nil in mu4e~guess-maildir (Fixes #472)

Add a guard so we don't error out if string-match evaluates to nil
Check for specific gmime-2.6 version (fixes #473)

Apparently, some gmime-2.5 versions match gmime-2.6 (pkgconfig) but
don't have the required API.

2.6.10 (2+ years old) is reported to work; test for this.
Some documentation fixes

(Thanks to Joe Corneli)
Bump version to 0.9.10
Rework getting database version (#469)

It seems we don't get the correct database version in some case with
some compilers, optimization flags. Suspecting some stale ->c_str().
Document that mu4e-maildir must not be a symlink ('fixes' #453)

mu doesn't support symlinks; document this. You can use hardlinks
instead of course.
Allow delete keybinding in console view-mode

Or, fix typo
Allow for gmime-2.6.7

See a86138a5. Apparently gmime 2.6.7 works fine as well.
Fix typo
Merge remote-tracking branch 'upstream/master'
Don't use g_clear_pointer yet, it's too new.

Do it the old way.
Add different face attribute for the mode-line

There is an additional face attribute for the mode-line.
Merge remote-tracking branch 'upstream/master'
Updated html export to org v8 standards

Replaced use of org-export-string with org-export-string-as to match
updated org coding standards.

This specifically addresses issue #391