Use std math functions in Max plugin.

VS12 provides math functions which were conflicting with ones defined
in texutil.h.  This removes the reliance on texutil.h and uses the
standard library's math in its place.
Add different SetText values to MaxCompat header.

Restores compilation of Max 7 plugin, as its SetText expects
a non-const pointer.

Additionally, NotifyInfo should already be declared in notify.h.