Reintroduce "Stop reaping children from SIGCHLD handler"

This re-introduces 3fe10692199fc20a5f4b6ac5057cce43babc5f36
with some associated fixes to address #1768.
expand: expand tilde to canonical paths

Work on #1133.
prompt_pwd: Use tilde expansion to get real full home path

Closes #1133.
Added hg repo status to robbyrussell example prompt
history: put the output through the pager in interactive mode

(Ideally, the behaviour of git could be implemented: pipe the input
through a pager iff the length is > window size and in interactive
mode).

Closes #1076.
contains: add documentation regarding the use of `--`

Closes #1194.

[skip ci]
Add Composer completion
Don't require .git before running git-describe

When calculating the version, we don't need to test for the presence of
.git before running `git describe`. This lets us work properly in a
detached work tree if GIT_DIR is set.
Fix 3rd arg to PROCESS_EXIT event for %self

The PROCESS_EXIT event takes 3 args: event name, pid, status. However,
when fish is exiting, the PROCESS_EXIT is instead given the status of
whether the last commandline parsed successfully. Change it to use the
same value that fish itself is going to exit with.
Update completion for Bundler

All commands and options available for Bundler version 1.7.4

Signed-off-by: David Adam <zanchey@ucc.gu.uwa.edu.au> (with trailing
fullstops removed)
Clean up some memory allocation in builtin_commandline
Eliminate wcsv2strv
Make C_ (gettext used in completions) return wcstring
Fix expansion tests on OS X
Fix C_ call to work when gettext is present
Set of fixes for issues identified by cppcheck
Remove a bunch of dead code identified by cppcheck
Don't suggest non-directories when tab completing cd

Fixes #1059
vi bindings: add CTRL-C handler in default mode

There is no CTRL-C handler for the default mode in the vi bindings. This makes it difficult to say "never mind" and start a new command line like you can do in bash's vi mode. 

There were CTRL-C handlers for insert and visual modes that go back to default mode, but nothing happens in default mode. I copy-pasted the CTRL-C handler from the default key bindings file.
Remove some more dead code