Enhanced callee resolution for decorators. Tests for decorators.

python/testData/psi/DecoratedFunction.py

@@ -0,0 +1,5 @@
+@staticmethod
+@xmlize(node="foo")
+def foo():
+  pass
+

python/testData/psi/DecoratedFunction.txt

@@ -0,0 +1,32 @@
+PyFile:DecoratedFunction.py
+  PyFunction
+    PyDecoratorList
+      PyDecorator: @staticmethod
+        PsiElement(Py:AT)('@')
+        PyReferenceExpression: staticmethod
+          PsiElement(Py:IDENTIFIER)('staticmethod')
+      PsiWhiteSpace('\n')
+      PyDecorator: @xmlize
+        PsiElement(Py:AT)('@')
+        PyReferenceExpression: xmlize
+          PsiElement(Py:IDENTIFIER)('xmlize')
+        PyArgumentList
+          PsiElement(Py:LPAR)('(')
+          PyKeywordArgumentImpl: node
+            PsiElement(Py:IDENTIFIER)('node')
+            PsiElement(Py:EQ)('=')
+            PyStringLiteralExpression: foo
+              PsiElement(Py:STRING_LITERAL)('"foo"')
+          PsiElement(Py:RPAR)(')')
+    PsiWhiteSpace('\n')
+    PsiElement(Py:DEF_KEYWORD)('def')
+    PsiWhiteSpace(' ')
+    PsiElement(Py:IDENTIFIER)('foo')
+    PyParameterList
+      PsiElement(Py:LPAR)('(')
+      PsiElement(Py:RPAR)(')')
+    PsiElement(Py:COLON)(':')
+    PsiWhiteSpace('\n  ')
+    PyStatementList
+      PyPassStatement
+        PsiElement(Py:PASS_KEYWORD)('pass')