Fix calc man page \-escape, add cal/comma.cal

Fixed a \-escape bug in calc(1) man page.

Added cal/comma.cal:

    Convert numbers into strings with 3-digit group and integer-fraction
    separators.

    If the value is an integer, the integer-fraction separator is not used.

    str_comma(x, [group, [decimal]])

	Convert x into a string.

	If group is given and is a string, group will be used as
	the 3-digit group separator, otherwise the default 3-digit
	group separator will be used.

	If decimal is given and is a string, group will be used as
	the integer-fraction separator, otherwise the default
	integer-fraction separator will be used.

	The decimal and group arguments are optional.

    set_default_group_separator(group)

	Change the default 3-digit group separator if group is a string,
	otherwise the default 3-digit group separator will not be
	changed.  Return the old 3-digit group separator.

    set_default_decimal_separator(decimal)

	Change the default 3-digit group separator if decimal is a
	string, otherwise the default integer-fraction separator
	will not be changed.  Return the old integer-fraction separator.

    print_comma(x, [group, [decimal]])

	Print the value produced by str_comma(x, [group, [decimal]])
	followed by a newline.

	If the str_comma() does not return a string, nothing is printed.

	The decimal and group arguments are optional.

	The value produced by str_comma() is returned.

    fprint_comma(fd, x, [group, [decimal]])

	Print the value produced by str_comma(x, [group, [decimal]]),
	without a trailing newline, on file fd.

	If the str_comma() does not return a string, nothing is printed.

	If fd is not an open file, nothing is printed.

	The decimal and group arguments are optional.

	The value produced by str_comma() is returned.

calc.man

@@ -596,7 +596,7 @@ may have to be replaced by:
 .sp 1
 .in +5n
 .nf
-print 27! ^2	or	print 27\!^2
+print 27! ^2	or	print 27\\!^2
 .fi
 .in -5n