I think this makes sense to have because we often have properties that are
very long and make the debug dump hard to read (RTP, codec_data, ...).

I've made this unconditional in this patch, but we probably want to control
this via GstDebugGraphDetails. Unfortunately that enum is not extensible, so
the options I see are:

1. Add a GST_DEBUG_GRAPH_SHOW_REALLY_ALL or something like that which is a
   '-1' value, making it future-proof. Then we can have something to control
   printing properties or truncating as a new flag. We could adjust this enum
   in the next API break and replace _REALLY_ALL with just _ALL.

2. Add a new flag after GST_DEBUG_GRAPH_SHOW_ALL. In this case, either we'd
   either have to have truncated as a default and the flag as an enabler for
   full output making the _ALL value not actuall be _ALL, or we'd have to have
   the flag after _ALL be a disabler and have it on by default (and any future
   additions would also have to be disablers, not enablers).

I prefer the first to the second because I think truncation (or even disabling
properties) is a sensible default over printing them out.

Opinions and other options welcome. :)