Nerfed diseases v5 from Thistleknot

From http://www.bay12forums.com/smf/index.php?topic=133312.msg4803130#msg4803130

* Reduced the % chance of certain diseases considerably...
    * Dwarves can now use their disease_resistance against catching the disease (i.e. via spreading), also the spreading is nerfed by reducing it's chance from 100% spreading to nearby dwarf's to a reduced % (60% for influenza, 25% for [visible] plagues).
    * Also, resistance is used against specific applications of the diseases (i.e. sub syndromes of a disease, ex... necrosis of the liver is resistable).
* If a dwarf suffered from an epidemic (i.e. influenza, meningitis, or pnuemonia) they are immune from catching the disease for up to one year, does away with the need for mutations.
* Medicine now acts as a vaccine for epidemics for one year.
* Plague Immunity (v5): Now dwarf's have a resistance chance * 2% of being immune to all plagues/rabies
* Medicine now has slightly extended durations against non communicable diseases, (i.e. blood pressure)  (needed only 3 times a year vs 5.22 times a year for full coverage).