'main': Fix the new 'backslash' test on zsh-5.0.2 and older.  (The bug occurred on zsh-5.0.7 and older but I don't have zsh-5.0.7 handy to test on.)
'main': Fix the new 'backslash' test on zsh-5.0.2 and older.  (The bug
occurred on zsh-5.0.7 and older but I don't have zsh-5.0.7 handy to test
on.)

Evidently, the issue was due to elision.

This addresses #665.0 and #665.5.

P71/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,x-way/zsh-syntax-highlighting,x-way/zsh-syntax-highlighting