Better error messages for the namespace argument

Work around when the first arg is -1

When seemingly valid arguments are given for non existent classes,
return a meaningful error message.
Described *1-*3,*e in repl-welcome

I have learned only by chance about the fact that REPL stores evaluation results in *1 - *3 and the last exception in *e. I am certainly not the only one unaware of this so it would be good to include it in the welcome message.

(For random visitors: they are defined in clojure's [`./src/clj/clojure/main.clj`](https://github.com/clojure/clojure/blob/master/src/clj/clojure/main.clj).)
Merge pull request #1312 from kumarshantanu/master

fix #1309 - lein.bat now honors HTTP_CLIENT env var
Add ^:skip-aot as default for app template.

Elaborate more on when ^:skip-aot will disable compilation. Would be
great to cut out a lot of that documentation for 3.0.0.
Fix a bug where specified repl host was ignored.
Remove usage of soon-to-be legacy API in nrepl.
Allow default eval-in dispatch value to be changed with a defmethod.
Handle stdin for :eval-in :nrepl.
Slight clarification to checkout dependency usage
`lein install` may not be needed if `lein` can find the library in another
repository.
Merge pull request #1313 from coventry/clarify-checkout-dependency-usage

Slight clarification to checkout dependency usage
Implement `lein deps :plugin-tree`, closes #1314.
Add in a :plugin-tree test.
Add alias explanations for `lein help task`.

Closes #1316.
Don't add alias-help as public API in lein.help.

Also add in a couple of tests to ensure that aliases print docstrings.
Added support of maven plugins in project.clj.

It's possible to add definition :plugins in project definition.
Example: 
 :plugins [[com.theoryinpractise/clojure-maven-plugin "1.3.13"]
           [org.apache.tomcat.maven/tomcat7-maven-plugin "2.1"]]
Maven plugins are now supported by :pom-plugins to avoid name conflict
with Leiningen :plugins vector. 

Added maven <configuration/> tag inside of plugin definition.

Added usecase of :pom-plugins in sample.project.clj
Fix tutorial repl message. Addresses #1317.
Use more descriptive local name.
Use profile-scoped targets in app template.