Jamroot: make release the default build

* `b2` will now build the release variant, unless you specify `b2 debug` in the command line.
* `b2 test` will still build the debug variant by default and there is no way to run it in release mode (enforced)

fixes #128

Jamroot

@@ -3,13 +3,15 @@ project gamgee
         <cxxflags>-std=c++1y
         <linkflags>-std=c++1y
         <warnings-as-errors>on
+    : default-build
+        <variant>release
   ;
 
   use-project /gamgee/libs : lib ;
 
   lib gamgee 
     : [ glob-tree *.cpp : .git test lib bin dox build ] /gamgee/libs//hts
     : <link>static 
-    :
+    : 
     : <include>.
   ;

test/Jamfile

@@ -4,5 +4,5 @@ lib boost_unit_test_framework ;
 run [ glob *.cpp ] /gamgee//gamgee /gamgee/libs//hts boost_unit_test_framework 
     : 
     : 
-    : <define>BOOST_ALL_DYN_LINK <threading>multi <include>../gamgee
+    : <define>BOOST_ALL_DYN_LINK <threading>multi <include>../gamgee <variant>debug
     : run ;