*.c: Localize variables

[schwehr]

• Move local variables closer to where they are use
• Combine definition and initialization when possible
• Add const when possible.

Skipped cases that were not immediately obvious.

[schwehr]

The Mac osx build:

../../bin/makegeo.c:29:6: error: variable 'gtif' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
        if (!tif) goto failure;
            ^~~~
../../bin/makegeo.c:50:6: note: uninitialized use occurs here
        if (gtif) GTIFFree(gtif);
            ^~~~
../../bin/makegeo.c:29:2: note: remove the 'if' if its condition is always false
        if (!tif) goto failure;
        ^~~~~~~~~~~~~~~~~~~~~~
../../bin/makegeo.c:31:2: note: variable 'gtif' is declared here
        GTIF *gtif = GTIFNew(tif);  /* GeoKey-level descriptor */
        ^