[expr] numeric equality operator

Uses string equality if either of the arguments cannot be interpreted as numeric, but if you actually want [string equal]ity, use the [eq] operator instead.

======
% expr {  1 == 2  }
0
% expr {  1 == 1  }
1
% expr {  0x1f == 31  }
1
======

To show you should be careful comparing floats:
======
% expr { 1 == 1.0000000000000001110223 }
1
======

Comparing with zero is a lot safer:
======
expr { 0 == 0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 }
0
======
but
======
expr { 0 == 0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 }
1
======

So from 1E-324 Tcl does not see the difference with zero any-more.


To write it a bit more clear:
======
% expr { 0 == 1E-323 }
0
% expr { 0 == 1E-324 }
1
======


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