Rename the test cases to run in specific orders

This way we can be fairly certain we run tests of lower-level
parts of the library before we run tests of higher-level more
complex parts.  If there is any problem in a lower-level part
of the library, the earlier test will identify it and stop,
making it easire to troubleshoot the failure.

A rough naming guide has been added for the test suite to
explain the current category structure.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

tests/NAMING

+Test sources should be named:
+
+  t????-function.c
+
+where ???? is a four digit code.  The first two digits classify
+the test into a major category; the final two digits indicate the
+sequence of the test within that category.  The function part of
+the test name should give a rough indication of what it does.
+
+Categories
+----------
+
+00__: Core library routines based only on the standard library,
+      and that are essential for everything else to run.  E.g.
+      errno and malloc.
+
+01__: Basic hashing functions, needed to handle the content
+      addressable store.
+
+02__: Basic object read access.