py/repl: Check for an identifier char after the keyword.

- As described in the #1850.
- Add cmdline tests.
diff --git a/py/misc.h b/py/misc.h
index a1d3e1c..79a4c1c 100644
--- a/py/misc.h
+++ b/py/misc.h
@@ -123,6 +123,7 @@
 bool unichar_isprint(unichar c);
 bool unichar_isdigit(unichar c);
 bool unichar_isxdigit(unichar c);
+bool unichar_isident(unichar c);
 bool unichar_isupper(unichar c);
 bool unichar_islower(unichar c);
 unichar unichar_tolower(unichar c);