targets: adjust packages to use new specific targets semantics

Seamless translation from 'target=<generic>' to either
- target.family == <generic> (in methods)
- 'target=<generic>:' (in directives)

Also updated docs to show ranges in directives.

var/spack/repos/builtin/packages/jdk/package.py

@@ -71,8 +71,8 @@ class Jdk(Package):
     provides('java@8',  when='@1.8.0:1.8.999')
     provides('java@7',  when='@1.7.0:1.7.999')
 
-    conflicts('target=ppc64', msg='jdk is only available for x86_64')
-    conflicts('target=ppc64le', msg='jdk is only available for x86_64')
+    conflicts('target=ppc64:', msg='jdk is only available for x86_64')
+    conflicts('target=ppc64le:', msg='jdk is only available for x86_64')
 
     # FIXME:
     # 1. `extends('java')` doesn't work, you need to use `extends('jdk')`