less: improvements to verbose status messages

less: improvements to verbose status messages

Make verbose status messages (-m/-M flags) behave more like the
real `less` command:

- fix display of line numbers so they're correct whether lines are
  being truncated (-S flag) or wrapped.
- don't display total lines or percentage when lines are read from
  stdin:  we don't have that information until we reach EOF.  When
  we do reach EOF the additional information is displayed.
- when lines are read from a file count the total number of lines
  so that we can display percentages.  Counting lines is avoided
  until the information is actually needed.  If the user pages to
  EOF the separate read pass can be avoided entirely.

Fixes Bug 7586

function                                             old     new   delta
m_status_print                                       195     382    +187
safe_lineno                                            -      35     +35
reinitialize                                         172     182     +10
read_lines                                           675     685     +10
buffer_fill_and_print                                178     169      -9
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 3/1 up/down: 242/-9)            Total: 233 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>