gEDA-user: pcb documentation build patches

[Dan McMahill <dan@xxxxxxxxxxxx>]

A number of people have had various problems building PCB documentation 
from CVS sources.  I have just checked in several changes to help 
address these problems.

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Building from a distfile
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Nothing special should be needed.  You should end up with documentation 
and you should not need to worry about having certain tools available 
just for building the docs.

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Building from CVS
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You should either

a)  use --disable-doc to prevent building any docs

or

b)
  i)  use --enable-maintainer-mode which will turn on some
      extra dependency rules for the documentation (normally
      not in place so building from a distfile is easy).

  ii) make sure you have version 4.6 or newer of texinfo
     (run makeinfo --version to check)

  iii) make sure you have latex installed

  iv)  make sure you compile in the png HID to pcb (this is
       enabled by default).


As part of the changes, the build system should fail more gracefully if 
you, for example, forget to install latex.  I have also included some 
checks for a new enough texinfo at configure time.  Now if you are in 
maintainer mode and have requested a build of the documentation, 
configure will fail with an informative message if you don't have the 
right tools.

------------------------
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Hope this helps out.

-Dan