issue producing pdf from tex

```
I tried many time to produce the pdf example with "python demo_context.py", under the "examples" folder, but I always get an error.

I thought it was a bug, and I have wait months in order to see it fixed... but
today I took a look at the source and I realize that in my debian squeeze is
missing the "context" module!

If Relatorio don't find "texexec" executable it produce an "obscure" error
message, look at here here:

$ python demo_context.py
generating output_basic.pdf...
Traceback (most recent call last):

File "demo_context.py", line 12, in

content = report(o=inv).render().getvalue()

File "/usr/lib/python2.5/site-packages/relatorio-0.5.5-py2.5.egg/relatorio/templates/base.py", line 36, in render

return self.serializer(self.events)

File "/usr/lib/python2.5/site-packages/relatorio-0.5.5-py2.5.egg/relatorio/templates/pdf.py", line 61, in call

cwd=self.working_dir)

File "/usr/lib/python2.5/subprocess.py", line 457, in check_call

retcode = call(*popenargs, **kwargs)

File "/usr/lib/python2.5/subprocess.py", line 444, in call

return Popen(*popenargs, **kwargs).wait()

File "/usr/lib/python2.5/subprocess.py", line 594, in init

errread, errwrite)

File "/usr/lib/python2.5/subprocess.py", line 1153, in _execute_child

raise child_exception

OSError: [Errno 2] No such file or directory

I propose to check if the "texexec" exists or to catch this error in order to
explain the problem ("'texexec' not found" or similar)

Thanks
Alessandro

```

Original issue reported on code.google.com by `cedric.krier@b2ck.com` on 8 Jul 2013 at 4:49

Start with examples/demo_context.py and the PDF serializer in relatorio/templates/pdf.py, then reproduce the command `python demo_context.py` with `texexec` unavailable. Trace the subprocess failure and make the missing executable produce a clear error instead of the obscure OSError; verify the example reports that `texexec` was not found.

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