#6 elimination of clang 3.3 warnings

[Jack Howarth]

Currently Clang 3.3 (Apple Clang 5.0) generates a large number of warnings when compiling pymol r4039. The attached patch eliminates those due to too few parentheses for assignments in conditionals or too many parentheses for equalities in conditionals. A number of recommendations for missing parentheses in complex conditionals are also added per the clang compiler warning recommendations. Also a number of missing initializations are added as recommended by the clang compiler warnings. Lastly a couple of instances where the conditional tests are always true (because unsigned variables are used) are eliminated.

[Thomas Holder]

applied the parts which looked like real bugs, but disregarding everything which is just about coding style.