Improve Lua support in etags

Improve Lua support in etags

* lib-src/etags.c (Lua_functions): Skip spaces before looking for
"function".

* etc/NEWS: Mention improved Lua support by 'etags'.

* test/etags/lua-src/test.lua (test): Add tests for indented
function definitions.
* test/etags/ETAGS.good_1:
* test/etags/ETAGS.good_2:
* test/etags/ETAGS.good_3:
* test/etags/ETAGS.good_4:
* test/etags/ETAGS.good_5:
* test/etags/ETAGS.good_6:
* test/etags/CTAGS.good: Adapt to the modified Lua tests.