display question: should ^N and \NNN widths be fixed?

[Thien-Thi Nguyen]

in src/indent.c `current_column', ^N and \NNN are presently hard coded
as taking 2 and 4 columns, respectively.  i'd like to propose that these
always be displayed in a fixed-width font, to avoid having to compute
their display widths.  this is not a big deal for ^N, but to compute
width of \NNN efficiently could mean another cache.

from user perspective, it seems to me ^N or \NNN as fixed width makes
reading them easier.

thi