df: Rewrite virt-df in C.

I have diffed the output from the original virt-df with this
new version, and they agree very closely.  Some differences:

 - Old virt-df have a divide-by-zero error in cases where the
   number of used inodes was 0.  New virt-df fixes this.

 - New virt-df uses gnulib human_readable library which displays
   numbers to 3 significant figures for -h output (old version
   used an ad hoc function).

1 files changed, 17 insertions, 0 deletions

diff --git a/df/README b/df/README
new file mode 100644
index 00000000..f928f2d8
--- /dev/null
+++ b/df/README
@@ -0,0 +1,17 @@
+This is the third rewrite of the virt-df program.  It very much
+follows the outline of the Perl program which this replaced in
+libguestfs 1.7.14.
+
+main.c -    main program
+
+domains.c - dealing with libvirt, only used if libvirt is around
+            at compile time
+
+df.c -      getting the stats from libguestfs
+
+output.c -  writing the output, CSV output
+
+virt-df.h - header file
+
+Note this also uses the shared options parsing code in
+'fish/options.[ch]'.