disable automatic build of examples

except if in maintainer mode
don't resolve disk-device symlinks

* enable symlink resolving when mnttab points to somewhere in /proc or user
  or packager enables it manually
fix man-page build configuration
add device_canonical for resolved device_name

If, however, necessary to resolve a device path, the resolved fqpn is
stored in device_canonical attribute. Otherwise, device_canonical
contains the same value as device_name.
prove whether setvbuf or a fallback is available

XPG6 specifies setvbuf for configuring stdio streams buffering behavior.
When no setvbuf is available, check for existence of setlinebuf which
could be a reasonable fallback.
ensure buffers are reasonable flushed

When a reasonable way to configure stdio streams being line buffered,
configure them. Otherwise flush after all desired stats are printed.
change default logging behavior from check to no
Display new device_canonical field.

A new field has been added to the filesystem statistics in libstatgrab.
The device_canonical field holds the real device name after resolving
symlinks. The original device_name field remains unchanged and holds
whatever is given by the operating system. When device_name is not a
symlink both fields are the same.

Here's an example of where it's useful:

/dev/disk/by-uuid/ee2f048d-68f6-428a-a95a-c949d3c05d67 -> ../../sda2

In this case, device_name contains the left-hand side and
device_canonical contains "/dev/sda2".