[Serusers] Manipulate from_uri

[Richard]

> The functionality will be included in avpops, but I cannot give an exact
> time line right now. There are a lot of operations that can be performed
> with avps and I should make a list with priorities, perhaps math
> operations with integers and string concatenation would be the first.
> Also, conversions from int to string and vice-versa...
> 

string concatenation is probably the most valuable.

math with integer, can't think of an application.

conversions between int and string, would it be transparent to user? For
example, inv-timeout uses int value. In avp_write("16", "s:inv-timeout"), we
didn't specify if 16 is a number or not, is it string by default? Also in
the db table, avp type is 0, meaning string value. We haven't encountered
any problem.

Thanks,
Richard