Delete trailing whitespace in src/

This needs doing periodically, and is best done to a whole bunch of files
at once.

Improve error reporting for the Arbnum string parsing functions.

Previously

Arbnum.fromHexString "g"

would raise Option and

Arbnum.fromHexString "ag"

would return 10. Now both fail with a "String not HEX" message.

Some basic evaluation support for square roots over ``:num`` and ``:real``. Also add syntax support for transcTheory.

Tidied up logrootScript.sml. The evaluation theorems for ``ROOT 2`` were present but they weren't being used.

Over the reals a conversion is used -- this will only work for rationals built from perfect squares. For example:

> EVAL ``sqrt (9 / 16)``
val it = |- sqrt (9 / 16) = 3 / 4: thm

The PolyML version now uses PolyML's builin IntInf support. (This change
doesn't appear to speed up HOL, but it's nice to have anyway.)