* lisp/calculator.el: more improvements and bugfixes.

* lisp/calculator.el: more improvements and bugfixes.

- Mark `calculator-paste-decimals' as obsolete.  (It wasn't having an
  effect anyway.)

- Simplify `calculator-number-to-string' by throwing most of the work
  onto `number-to-string', leaving just some tweaks for decimal inputs.
  This leads to some minor changes, for example, pasting "1x1" in hex
  mode would warn that "x" is ignored and result in "11" (and it wasn't
  done in decimal mode), whereas now it just ignores everything from the
  "x" and on and result in a "1" just like in decimal input mode.  Also,
  overflows are left for `number-to-string' to deal with.

- `calculator-paste' is very simple as a result.

- Extend the simplified `calculator-paste': with a prefix argument it
  pastes a string as if the characters were entered.  This can be used
  to reduce expressions, but note that it's a simple literal operation,
  so precedence can be messed, a number can be paster while entering a
  number, spaces and newlines matter, etc.

- Fix a minor bug where "e+" in hex mode wouldn't use "+" as an
  operator.

- Fix a bug in `calculator-put-value': avoid grouping in the display
  that is used to construct `calculator-curnum'.  This would trigger
  when pasting or getting a value from a register in some radix mode
  with a large enough value.  Another fix: make the output radix equal
  the input one, otherwise numbers could be converted twice.