[Xastir] Tigermap - intensity

[Reuven Z Gevaryahu]

I can confirm that after upgrading to imagemagick 5.5.4 the tigermap 
intensity broke. It worked fine with the older imagemagick when I tested 
it a few weeks ago, and I don't think anything major in that section of 
the code has changed. (I also doubt it's related to the configure 
changes). I'm just seeing no difference between 50 and 100, nothing 
strange like described though.

--Reuven (KB3EHW)