Complete quoting for parameters in "configure.ac"

[elfring]

I suggest to be more explicit where macro expansion will not be required in the current build configuration script.

[zdenop]

Please make a pull request or send the patch.

[amitdo]

@stweil
Do you think we need to fix something in the current configure.ac as suggested here? If the answer is 'yes', please send a PR.

[stweil]

PR #335 should fix this issue. I tested my patch like this:

# Save old configure.
mv configure old-configure
# Apply my patch.
...
# Create new configure.
autoconf
# Compare old and new configure. There should be only whitespace changes.
diff -u --ignore-space-change old-configure configure