Context help for "e" shows help for "erf" instead

Typing “e” and then pressing F1 for context help doesn’t show help for the constant “e”. Instead it shows help for the function “erf”.

This is a consequence of Editor::getKeyword calling Editor::matchFragment internally which effectively does a a prefix autocomplete. This always autocompletes “e” to “erf” before passing “erf” to the docs viewer.