Definite integrals

`ALIAS` offers various procedures to determine bounds for the value of
definite integrals with one or more variables.
Some of them involve the use of the derivatives and you should be
careful when the interval evaluation of these derivative cannot be
performed. For example when considering
you should
not 0 in the integration domain. In that case you should integrate
around 0 by using the `Integrate` problem while using another
procedure for the remaining part of the domain.

Jean-Pierre Merlet 2012-12-20