Add type-safe headerPutFoo() methods for supported tag data types

Add type-safe headerPutFoo() methods for supported tag data types
- requiring all access through rpmtdFromFoo() just adds unnecessary
  indirection and pain for little gain, the header is fairly intelligent
  when it comes to inserting data
- this gives us various benefits over the old headerAddEntry() interface too:
  + basic type checking done by compiler
  + extra sanity checking (ie you can't add string data to integer tags,
    don't permit adding more than one entry to non-array data etc)
  + "do the right thing" approach - add / append as needed and supported
    by various types
  + headerPutString() can now be used on both single strings and string
    arrays making the interface much nicer for the rather common case of
    appending strings one by one to string array tags