Stronger checks on command-line build request.

    * new/property.jam (validate): New rule.
    * new/build-request.jam (convert-command-line-element): Call
        property.validate for each build request element.


[SVN r14304]

tools/build

@@ -1 +1 @@
-Subproject commit 29af4a572f9fc81f0f54b462984e75269aab7267
+Subproject commit 3555e628b5dd8a38de7abf81a9a3d9d259d74a83