Avoid passing more than one instance of ERL_LIBS to child processes

This commit fixes issue #98 by removing the ERL_LIBS and REBAR_DEPS_DIR
from the list of environment variables exported by the rebar_port_compiler
plugin.
Incorrect REMSH args when sname is used

When a node is configured with -sname in app.config or sys.config the
REMSH_NAME_ARG and REMSH_REMSH_ARG arguments are incorrect due the
assumption that the node name always contains '@'.

To fix the bug, the script tries to find '@' and then compose the
arguments acording to node name type. If in long name mode the
script can't compose a correct node name exits with warning.
Make REMSH node run in hidden mode

To avoid problems with REMSH node being visible from another nodes
starts it in hidden mode (erl -hidden).
Allow specification of module dependencies for appups

The order in which modules, within an application, are loaded can be
important. This patch adds allows the specification of module
dependencies such that generate .appup/.relup scripts will load a
module's dependent modules before itself.

To use:

in rebar.config, add a module_deps

{module_deps, [{ModuleName, [DependentModuleName, ...]}]}.

ModuleName is the name of any module, followed by a list of module
names that it depends on.
Add test for regression caused by 252b31f (#90)
rebar_core: minor comment fix
Fix regression caused by 252b31f (#90)
inttest/depplugins: update docs
Adapt erlydtl compiler plugin to latest version of erlydtl
Use proplists:unfold to make sure we feed a proplist to keymerge.
{ok, Module} is an acceptable return value from do_compile.
eunit: fix dialyzer warnings introduced in 03da5e0b
Merge pull request #221 from kaos/erlydtl

Adapt erlydtl compiler plugin to latest version of erlydtl
Document support for abbreviated commands
Mention rebar -c/--commands
Merge pull request #232 from tuncer/doc-abbrev-cmd

Document support for abbreviated commands
Merge pull request #230 from tuncer/fix-dialyzer-warnings

eunit: fix dialyzer warnings introduced in 03da5e0b
docs: fix #228
Merge pull request #233 from tuncer/commands

docs: fix #228
Speed up the compilation process

* Do not parse source files twice while checking for relationship.
* Keep files relationships in a graph.
* The option 'keep_build_info' is introduced. When set to 'true'
  the graph will be kept in ebin/.rebar.build.info and will be
  used by further compiler calls. The default is 'false'.