Fix: Placed all +build tags in the same location
Fix: Split CFLAGS, LDFLAGS into seperate lines for readability and lookup
Fix: Placed empty line between copyright comments and build tags for readability
Fix: Placed OS specfic cgo flags at the end if the cgo sections contains multiple lines.
The SQLiteConn.RegisterAggregator implementation was defined in
sqlite3_trace.go file, which is guarded with a build constraint. This
change simply moves RegisterAggregator to the main sqlite3.go file,
and moves accompanying unit tests.
The rationale for this move is that it was not possible for downstream
using packages to use RegisterAggregator without also specifying (and
notifying the user) the 'trace' build tag.
