Add new example.

[SVN r21665]

v2/example/variant/Jamfile

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+
+# By default, build the project with two variants
+# we've defined in project-root.jam
+project
+    : default-build crazy super_release
+    ;
+
+exe a : a.cpp libs//l ;
+

v2/example/variant/a.cpp

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+
+void l();
+int main() { l(); return 0; }

v2/example/variant/libs/Jamfile

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+
+lib l : l.cpp ;

v2/example/variant/libs/l.cpp

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+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+void l() {}

v2/example/variant/project-root.jam

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+
+# Define a build variant which is just combination
+# of four properties. 
+variant crazy : <optimization>speed <inlining>off 
+                <debug-symbols>on <profiling>on ;
+		
+# Define a built variant inherited from 'release'.
+# It defines one new property and get all properties
+# from parent variant.		
+variant super_release : release : <define>USE_ASM ;

v2/example/variant/readme.txt

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+
+This example shows how user can create his own build variants.
+Two variants are defined: "crazy", which is just random combination
+of properties, and "super-release", which is inherited from "release",
+and differs by a single define.
+
+See the project-root.jam for the definitions.