Add 'generate-appups' command

To further support OTP releases I have added support for generating
application appup files. These include instructions that systools uses
to generate a relup file which contains the low level instructions
needed to perform a hot code upgrade. My goal with this module is to
produce "good enough" appup files or at least a skeleton to help one get
started with something more complex. If an appup file already exists for
an application this command will not attempt to create a new one.

Usage:
$ rebar generate-appups previous_release=/path/to/old/version

Generally this command will be run just before 'generate-upgrade'.

1 files changed, 2 insertions, 0 deletions

diff --git a/ebin/rebar.app b/ebin/rebar.app
index 1f7db21..a99df4e 100644
--- a/ebin/rebar.app
+++ b/ebin/rebar.app
@@ -3,6 +3,7 @@
   {vsn, "2"},
   {modules, [ rebar,
               rebar_abnfc_compiler,
+              rebar_appups,
               rebar_app_utils,
               rebar_base_compiler,
               rebar_config,
@@ -80,6 +81,7 @@
                               ]},
 
                     {rel_dir, [
+                               rebar_appups,
                                rebar_reltool,
                                rebar_upgrade
                               ]}