add coverage test for travis

.coveragerc

@@ -0,0 +1,8 @@
+[run]
+branch = True
+source = sklearn
+include = */sklearn/*
+omit =
+    */sklearn/externals/*
+    */benchmarks/*
+    */setup.py

.gitignore

@@ -35,6 +35,8 @@ samples
 doc/coverages
 doc/samples
 *.prof
+.tox/
+.coverage
 
 lfw_preprocessed/
 nips2010_pdf/

.travis.yml

@@ -1,4 +1,6 @@
 language: python
+env:
+    - COVERAGE=--with-coverage
 python:
     - "2.7"
 virtualenv:
@@ -7,4 +9,8 @@ before_install:
     - sudo apt-get update -qq
     - sudo apt-get install -qq python-scipy python-nose
 install: python setup.py build_ext --inplace
-script: make test
+	 - if [ "${COVERAGE}" == "--with-coverage" ]; then
+      	   sudo $PIP install coverage;
+      	   fi
+script: - make test
+    	- if [ "${COVERAGE}" == "--with-coverage" ]; then make test-coverage; fi