[WIP] vim-patch:7.4.276

Because this patch involved factoring out some code into its own function, I think that it would be nice to add a unit test for `get_isolated_shell_name()` in `misc1.c`. However, I am unsure where to put the test. It seems that the functions in `misc1.c` likely to be refactored, so I don't know if I should create a new file or not. I am also unfamiliar with moonscript. Could I get some guidance before the patch is reviewed?