Improve python code indentation warning / error messages

Examples/test-suite/errors/swig_pythoncode_bad.stderr

@@ -1 +1 @@
-swig_pythoncode_bad.i:7: Error: Line indented less than expected (line 2 of pythoncode)
+swig_pythoncode_bad.i:7: Error: Line indented less than expected (line 2 of %pythoncode or %insert("python") block) as no line should be indented less than the indentation in line 1

Examples/test-suite/errors/swig_pythoncode_bad2.stderr

@@ -1 +1 @@
-swig_pythoncode_bad2.i:13: Error: Line indented less than expected (line 3 of pythoncode)
+swig_pythoncode_bad2.i:13: Error: Line indented less than expected (line 3 of %pythoncode or %insert("python") block) as no line should be indented less than the indentation in line 1

Examples/test-suite/errors/swig_pythoncode_bad3.i

@@ -0,0 +1,7 @@
+%module xxx
+
+%pythoncode %{
+  def extra():
+  	print "extra a" # indentation is 2 spaces then tab
+	  print "extra b" # indentation is tab then 2 spaces
+%}

Examples/test-suite/errors/swig_pythoncode_bad3.stderr

@@ -0,0 +1 @@
+swig_pythoncode_bad3.i:7: Warning 740: Whitespace indentation is inconsistent compared to earlier lines (line 3 of %pythoncode or %insert("python") block)