Megacommit of many files.
Mostly, several functions that take pointers as arguments, almost always char * pointers, had those pointers qualified with "const". Those that returned pointers to previously const-qualified arguments had their return values qualified as const. Some structure members were qualified as const to retain that attribute from the variables from which they were assigned. The macro DE_CONST is used to deal with a handful of very special places where something is qualified as const but really needs to have its const qualifier removed. rdata.c now defines macros for the prototypes of the basic rdata functions, and all of the lib/dns/rdata/**/*.c files now use them. Some minor integer-compatibility issues. (IE, ~0x03 is a signed int, so assigning it to an unsigned int should use a cast. The type of an enum member is int, so there are some conversion issues there, too.) A pointers-to-function should not be cast to a pointer-to-object. Variables should not be named for C reserved identifiers. One or two set-but-not-used variables removed. Minor other ISC style cleanups.
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