bug#24439: ispell.el; cutom setting `ispell-library-directory'; patch

[Laimonas Vėbra]

Hello,

On Windows if one uses cygwin ispell, then one should fix ispell LIBDIR 
(which is not correct absolute path) relative to cygwin root by setting 
`ispell-library-directory'. Or one also might wish to use custom 
location of dictionaries.
Currently ispell.el breaks this possibiliity, because it resets
`ispell-library-directory' to possibly incorrect or unwanted ispell 
LIBDIR on every ispell call. Suggested patch attached.

I'm not sure if it doesn't break something (that's why i'm asking in 
patch comments), but AFAICS it shouldn't.
Could someone familiar with ispell.el overview and comment on this tiny 
patch?

ispell.patch
Description: Text document