No check for gnuplot

[Didier Barvaux]

When building the library with --enable-rohc-stats, the configure script should check for the presence of the gnuplot tool. Otherwise, the generation of the stats fails.

Steps to reproduce:
1. Retrieve trunk sources
2. ./autogen.sh --enable-rohc-stats
3. make all

[Didier Barvaux (didier-barvaux)]

Reproduced on the 1.3.x branch by either:
 - make measures
 - make all && cd statistics/ && ./auto.pl && cd -

[Didier Barvaux (didier-barvaux)]

Reproduced on the 1.2.x branch by either:
 - make measures
 - make all && cd statistics/ && ./auto.pl && cd -

[Didier Barvaux (didier-barvaux)]

On the 1.3.x branch:
   Check for gnuplot presence in measures Makefiles.
   Remove the statistics scripts.

See http://bazaar.launchpad.net/~didier-barvaux/rohc/1.3.x/revision/162

[Didier Barvaux (didier-barvaux)]

On trunk, add a check for the gnuplot binary in the configure script.
See http://bazaar.launchpad.net/~didier-barvaux/rohc/main/revision/264

[Didier Barvaux (didier-barvaux)]

On the 1.2.x branch:
   Check for gnuplot presence in measures Makefiles.
   Check for gnuplot presence in statistics scripts.

See http://bazaar.launchpad.net/~didier-barvaux/rohc/1.2.x/revision/135