[expr] "raise to power" operator, similar to [pow] function

Returns an integer value if both arguments are integers, and [double]-precision floating-point otherwise.

The left operand may be any integer from Tcl's unlimited integer range.

The right operand is limited to a max integer value of 268435455 (0xfffffff) (28 bits).  (Unless the left operand is -1, 0, or 1, so that the answer is trivial).

Expect to wait a long while for [[expr 2**0xfffffff]] to return.

During early 2009, a thread broke out in the comp.lang.tcl usenet group discussing the observation that Tcl's calculation for 

======
puts [expr {-2**2}]
======

surprised someone who was expecting the same results as algebra (or even [perl]). Instead of the results being '''-4''' , Tcl returns '''4'''.
The reason has to do with the operator precedence between the [-] and '''**''' operators. 

[ZB] Either I can't count - feel free to correct me in such case - or indeed TCL is right: (-2)^2 = (-2)*(-2) = 4

So why such "surprise", actually?

[AMG]: `(-2)**2 = 4`, but `-(2**2) = -4`.

[LV] The issue is that, algebraically, the '''-''' is expected to bind last. I know '''I''' was surprised to learn that ... but it's been over 30 years since I was in a math class and I've grown to think of things as Tcl sees them rather than as apparently the math world sees them.

[RS] Even thornier, the issue.. in for example 2 * -3 you cannot but first apply the unary minus, then multiplication.

[AMG]: There are other disagreements over operator precedence.  [&] and [|] are quite nasty:

%|Expression   |Result|Comment                       |%
&|expr 5&2==2  |1     |expression without parentheses|&
&|expr 5&(2==2)|1     |actual behavior of Tcl and [C]|&
&|expr (5&2)==2|0     |naively expected behavior     |&

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%| [Category Operator] | [Category Command] | [Category Mathematics] |%
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