PATCH: Spell exp2l correctly

[Roland McGrath]

> What's the failure condition look like if you add a symbol to an old
> version?  I don't see why a new application linking against
> exp2l@GLIBC_2.4 would fare any differently than a new application
> linking against exp2l@GLIBC_2.1, but presumably there's a reason...

Version set dependencies are detected immediately at startup with a fairly
clear error, whereas a missing symbol can cause a crash that's not seen
until it's actually called (when recovering the error message might have
become more confusing).  In practice, you won't ever get as far as startup,
because packagers like rpm automatically represent version sets in the
package dependencies and so you can know before even attempting to install
your operating system that the provided glibc doesn't meet the requirements
of the given application package.