patch 8.1.2341: not so easy to interrupt a script programatically

Problem:    Not so easy to interrupt a script programatically.
Solution:   Add the interrupt() function. (Yasuhiro Matsumoto, closes #2834)

runtime/doc/eval.txt

@@ -1,4 +1,4 @@
-*eval.txt*	For Vim version 8.1.  Last change: 2019 Nov 21
+*eval.txt*	For Vim version 8.1.  Last change: 2019 Nov 24
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -2531,6 +2531,7 @@ inputrestore()			Number	restore typeahead
 inputsave()			Number	save and clear typeahead
 inputsecret({prompt} [, {text}]) String	like input() but hiding the text
 insert({object}, {item} [, {idx}]) List	insert {item} in {object} [before {idx}]
+interrupt()			none	interrupt script execution
 invert({expr})			Number	bitwise invert
 isdirectory({directory})	Number	|TRUE| if {directory} is a directory
 isinf({expr})			Number	determine if {expr} is infinity value
@@ -6181,6 +6182,19 @@ insert({object}, {item} [, {idx}])			*insert()*
 		Can also be used as a |method|: >
 			mylist->insert(item)
 
+interrupt()						*interrupt()*
+		Interrupt script execution.  It works more or less like the
+		user typing CTRL-C, most commands won't execute and control
+		returns to the user.  This is useful to abort execution
+		from lower down, e.g. in an autocommand.  Example: >
+		:function s:check_typoname(file)
+		:   if fnamemodify(a:file, ':t') == '['
+		:       echomsg 'Maybe typo'
+		:       call interrupt()
+		:   endif
+		:endfunction
+		:au BufWritePre * call s:check_typoname(expand('<amatch>'))
+
 invert({expr})						*invert()*
 		Bitwise invert.  The argument is converted to a number.  A
 		List, Dict or Float argument causes an error.  Example: >