Be more consistent in allowing the user to override use of the
temporary directory by specifying $TMPDIR.  Also prefer P_tmpdir
macro (defined in <stdio.h>) if that is defined, rather than
hard-coding "/tmp" for the fallback location.

The compiled PCRE regexps used for inspection were being leaked when
the library was unloaded.

(Found by valgrind).

This API is a simpler replacement for the guestfish commands
list-devices / list-partitions / lvs, in the case where you are
just examining a guest by hand to see what it contains.

Typical usage and output in guestfish is like this:

$ guestfish --ro -a /dev/vg_trick/F13x64
><fs> run
><fs> list-filesystems
/dev/vda1: ext4
/dev/vg_f13x64/lv_root: ext4
/dev/vg_f13x64/lv_swap: swap

It can also be used to replace programs that try to mount
devices to determine if they are mountable filesystems.

This commit converts (some of) the Perl inspection code to C and
makes it available through core APIs.  The new APIs are:

inspect-os        - Does the inspection, returns list of OSes
inspect-get-*     - Get results of the inspection

where '*' is one of:

  type            - 'windows' or 'linux'
  distro          - Linux distro
  arch            - architecture
  product-name    - long product name string
  major-version
  minor-version   - major.minor version of OS
  mountpoints     - get a list of the mountpoints
  filesystems     - get all filesystems associated with the OS

This works for all existing supported Linux and Windows OSes.

This change simply converts the existing Perl-only function
file_architecture into a core API call.  The core API call is
written in C and available in all languages and from guestfish.