stdenv/stripHash: print to stdout, not to variable

`stripHash` documentation states that it prints out the stripped name to
the stdout, but the function stored the value in `strippedName`
instead.

Basically all usages did something like
`$(stripHash $foo | echo $strippedName)` which is just braindamaged.
Fixed the implementation and all invocations.

doc/stdenv.xml

@@ -1231,13 +1231,12 @@ echo @foo@
     <term><function>stripHash</function>
     <replaceable>path</replaceable></term>
     <listitem><para>Strips the directory and hash part of a store
-    path, storing the name part in the environment variable
-    <literal>strippedName</literal>. For example:
+    path, outputting the name part to <literal>stdout</literal>.
+    For example:
     
 <programlisting>
-stripHash "/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
 # prints coreutils-8.24
-echo $strippedName
+stripHash "/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
 </programlisting>
 
     If you wish to store the result in another variable, then the
@@ -1245,7 +1244,7 @@ echo $strippedName
     
 <programlisting>
 name="/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
-someVar=$(stripHash $name; echo $strippedName)
+someVar=$(stripHash $name)
 </programlisting>
 
     </para></listitem>