tests: add test-check-execute.t

Try to prevent people from adding files with incorrect execute bits

tests/test-check-execute.t

@@ -0,0 +1,23 b''
+#require test-repo execbit
+
+  $ cd "`dirname "$TESTDIR"`"
+
+look for python scripts without the execute bit
+
+  $ hg files 'set:**.py and not exec() and grep(r"^#!.*?python")'
+  [1]
+
+look for python scripts with execute bit but not shebang
+
+  $ hg files 'set:**.py and exec() and not grep(r"^#!.*?python")'
+  [1]
+
+look for shell scripts with execute bit but not shebang
+
+  $ hg files 'set:**.sh and exec() and not grep(r"^#!.*(ba)?sh")'
+  [1]
+
+look for non scripts with no shebang
+
+  $ hg files 'set:exec() and not **.sh and not **.py and not grep(r"^#!")'
+  [1]