Function: sumnumalt
Section: sums
C-Name: sumnumalt0
Prototype: V=GGEDGD0,L,p
Help: sumnumalt(X=a,sig,s,{tab},{flag=0}): numerical summation of (-1)^X s
 from X = ceiling(a) to +infinity. Note that the (-1)^X must not be included.
 sig is either a scalar or a two-component vector coded as in intnum, and the 
 scalar part is larger than all the real parts of the poles of s. Uses intnum,
 hence tab is as in intnum. If flag is nonzero, assumes that the function to 
 be summed satisfies conj(f(z))=f(conj(z)), and then up to twice faster.

