Add const qualifier and explicit length
Fix problem with test47: addition is not bitwise OR

:diffsplit command used to include some flag value twice. If I was using bitwise 
OR it would be OK, but I had addition here. Hence I need to either somehow 
emulate bitwise OR in lua or make sure no such double inclusions happen. I have 
chosen to use the first variant: bitwise OR for flag values using lua metatables 
and addition.

Note: transform_ex_cmds_defs script was removed because I did not want to write 
updates to ex_cmds.lua there.