graph: allow RRD files to be missing

An option (-Z/--missing-ds) is added to allow RRD files to be
missing. In this case, the unknown value is assumed.
graph: when an RRD file is missing, provide an empty one

Instead of providing a RRD without any DS, we provide one with the
expected DS. This allows one to use CDEF with this RRD. The DS
contains only NaN values.
graph: rename --missing-ds to --use-nan-for-all-missing-data
Add prototype for bad_format_imginfo

This patch solve implicit declaration of function 'bad_format_imginfo'
warning introduced by commit 37d3050 "Added imginfo format check".

rrd_graph.c: In function 'rrd_graph_v':
rrd_graph.c:4025: warning: implicit declaration of function 'bad_format_imginfo'
rrd_graph.c:4025: warning: nested extern declaration of 'bad_format_imginfo'
rrd_graph.c: At top level:
rrd_graph.c:4836: warning: no previous prototype for 'bad_format_imginfo'
Allow empty imginfo string format

Commit 37d3050 "Added imginfo format check" breaks -f "" which used
to be very usefull to print data as text format on stdout. Allowing
an empty -f was particularly interesting because there was no
<width>x<height> printed out.

Before :

[root@nagios-2b ~]# rrdtool graph /dev/null -f "" --start -1d \
    DEF:d=/var/lib/rrd/nagios-2b/load.rrd:load5:AVERAGE \
    VDEF:v=d,AVERAGE \
    PRINT:v:%.6lf
5.284605

After :

[root@nagios-2b ~]# rrdtool graph /dev/null -f "" --start -1d \
    DEF:d=/var/lib/rrd/nagios-2b/load.rrd:load5:AVERAGE \
    VDEF:v=d,AVERAGE \
    PRINT:v:%.6lf
ERROR: bad format for imginfo
Merge pull request #402 from julthomas/jth/imginfo

Related to  37d3050 "Added imginfo format check"
doc: updated options / parameters

Signed-off-by: Jaroslav Škarvada <jskarvad@redhat.com>
Merge pull request #403 from yarda/yardas

doc: updated options / parameters
Fix median filter in cdeftutorial

Fixes commit 1198d31
What was described as an median filter was actually an average filter.

Sort the 3 values then take the middle of them using POP,EXC,POP.
Also uses one less prev() to decrease filter delay.

See https://en.wikipedia.org/w/index.php?title=Median_filter&oldid=558817813

Alternative fix is to rename "median" with "average" in the
description, but there already is an AVG rpn function for that.
Merge pull request #405 from ThomasHerrlin/thomasherrlin

Fix median filter in cdeftutorial
Fixed constant used in timespan check to be a long long.

This fixes a compiler warning on AIX in 32-bit with IBM XL C/C++ compiler.
fix format string in Ruby binding
Merge branch 'master' of github.com:oetiker/rrdtool-1.x
Remove wrong comma.
Merge pull request #412 from Zsub/patch-1

Remove wrong comma.
4294967296 has to be treaded as long long for this to work ... help the compiler see this
Add an option to let rrdcached recursively create directories.

If a `create` command is given, a path is accepted. This option enables rrdcached to create the directory structure if it does not exist yet.
Change tabs to spaces
bit patterns are 64bit, so better make sure they are 64bit on all platforms fix for issue 356
Upgrade Solution and Projects to VS2010