update type inferencing for conditionals / comparisons, to pick up the right dtype (int64 vs int32), as this is required for proper conversion of conditions in vector selects

modify emit_if / emit_vector_if such that they take the condition_mapper as an arguement, rather than the condition_str itself -- additionally, modify the condition_mappers such that they it can take an optional parameter that is the current inner AST to be wrapped in an if-statement

use iname_to_tags instead of iname_to_tag

See merge request inducer/loopy!258

Allowing multiple tags for inames

See merge request inducer/loopy!249

in order to get around the vector iname conditional issue, we have to fix this parameter before generating the kernel