BigDecimal#** shouldn't return Integer

[tompng]

BigDecimal#** is expect to return BigDecimal

/*  call-seq:
 *    self ** other -> bigdecimal
 *
 *  Returns the \BigDecimal value of +self+ raised to power +other+:
 * ...
 */

BigDecimal(123).power(10, 10)
# => 0.792594609605189126649e21 (BigDecimal) OK except too high precision
BigDecimal(123).power(10.5, 10)
# => 8790299449000000000000 (Integer) Questionable result

BigDecimal(123) ** BigDecimal('10.5')
#=> 0.879029945260967009185694434e22 BigDecimal, OK
# => 8790299449000000000000 (Integer) Definitely a bug.

BigMath.exp returning Integer is the cause.

# /* call-seq:
#  *   BigMath.exp(decimal, numeric)    -> BigDecimal

BigMath.exp(10, 5)
# => 22026 (Integer)
BigMath.exp(10, 6)
# => 0.220265e5 (BigDecimal)