Don't use htmlentities() to sanitize input/output.

Don't use htmlentities() to sanitize input/output.
It breaks things outside of Western Europe/US.

Changing functions to use htmlspecialchars(). It still breaks things
in compose, when is_conversion_safe($charset)=true.

at least it breaks less.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@7051 7612ce4b-ef26-0410-bec9-ea0150e637f0