This changes variable expansion so that it is recursive

tests/test1.golden

Index: tests/test1.golden
===================================================================
--- tests/test1.golden	(revision 0)
+++ tests/test1.golden	(revision 0)
@@ -0,0 +1,58 @@
+GENERAL: running with these options:
+GENERAL:   msvs_version: None
+GENERAL:   suffix: ''
+GENERAL:   includes: None
+GENERAL:   depth: '..'
+GENERAL:   generator_flags: []
+GENERAL:   formats: ['gypd']
+GENERAL:   debug: ['variables', 'general']
+GENERAL:   defines: None
+VARIABLES: Expanding 'import math; print math.pi' to 'import math; print math.pi'
+VARIABLES: Expanding 'ABCD' to 'ABCD'
+VARIABLES: Expanding 'python -c "print 'letters'"' to 'python -c "print 'letters'"'
+VARIABLES: Executing command 'python -c "print 'letters'"'
+VARIABLES: Expanding '<!(python -c "print 'letters'")' to 'letters'
+VARIABLES: Expanding '<(<!(python -c "print 'letters'"))' to 'ABCD'
+VARIABLES: Expanding 'pi' to 'pi'
+VARIABLES: Expanding '["python", "-c", "<(pi)"]' to '["python", "-c", "import math; print math.pi"]'
+VARIABLES: Executing command '['python', '-c', 'import math; print math.pi']'
+VARIABLES: Expanding '<!(["python", "-c", "<(pi)"])' to '3.14159265359'
+VARIABLES: Expanding 'letters' to 'letters'
+VARIABLES: Expanding 'python -c "print '<(letters)'"' to 'python -c "print 'ABCD'"'
+VARIABLES: Executing command 'python -c "print 'ABCD'"'
+VARIABLES: Expanding '<!(python -c "print '<(letters)'")' to 'ABCD'
+VARIABLES: Expanding 'letters' to 'letters'
+VARIABLES: Expanding 'letters' to 'letters'
+VARIABLES: Expanding 'pi' to 'pi'
+VARIABLES: Expanding 'python -c "<(pi)"' to 'python -c "import math; print math.pi"'
+VARIABLES: Executing command 'python -c "import math; print math.pi"'
+VARIABLES: Expanding 'python -c "print '<!(python -c "<(pi)") <(letters)'"' to 'python -c "print '3.14159265359 ABCD'"'
+VARIABLES: Executing command 'python -c "print '3.14159265359 ABCD'"'
+VARIABLES: Expanding '<!(python -c "print '<!(python -c "<(pi)") <(letters)'")' to '3.14159265359 ABCD'
+VARIABLES: Expanding 'foo' to 'foo'
+VARIABLES: Expanding 'none' to 'none'
+VARIABLES: Expanding 'test_action' to 'test_action'
+VARIABLES: Expanding 'echo' to 'echo'
+VARIABLES: Expanding '_inputs' to '_inputs'
+VARIABLES: Expanding 'var2' to 'var2'
+VARIABLES: Expanding '<(var2)' to '3.14159265359 ABCD'
+VARIABLES: Expanding '<(_inputs)' to '"3.14159265359 ABCD"'
+VARIABLES: Expanding '_outputs' to '_outputs'
+VARIABLES: Expanding 'var4' to 'var4'
+VARIABLES: Expanding '<(var4)' to 'ABCD'
+VARIABLES: Expanding '<(_outputs)' to 'ABCD'
+VARIABLES: Expanding '3.14159265359 ABCD' to '3.14159265359 ABCD'
+VARIABLES: Expanding 'ABCD' to 'ABCD'
+VARIABLES: Expanding 'test1.gyp' to 'test1.gyp'
+VARIABLES: Expanding 'ABCD' to 'ABCD'
+VARIABLES: Expanding '3.14159265359' to '3.14159265359'
+VARIABLES: Expanding 'ABCD' to 'ABCD'
+VARIABLES: Expanding '3.14159265359 ABCD' to '3.14159265359 ABCD'
+VARIABLES: Expanding 'foo' to 'foo'
+VARIABLES: Expanding 'none' to 'none'
+VARIABLES: Expanding 'test_action' to 'test_action'
+VARIABLES: Expanding 'echo' to 'echo'
+VARIABLES: Expanding '"3.14159265359 ABCD"' to '"3.14159265359 ABCD"'
+VARIABLES: Expanding 'ABCD' to 'ABCD'
+VARIABLES: Expanding '3.14159265359 ABCD' to '3.14159265359 ABCD'
+VARIABLES: Expanding 'ABCD' to 'ABCD'