Remove find-java-rt-jar.sh, document how -b interacts with older JDKs

* Remove the use of the `find-java-rt-jar.sh` script in CI, as this is no
  longer necessary with the advent of `--java-bin-dirs`/searching the `PATH`
  for Java. This fixes #1061.

* On a related note, it turns out that SAW's approach to detecting where
  `rt.jar` lives likely doesn't work on pre-7 JDKs on macOS. Given how
  ancient these versions of Java anymore, let's just document this infelicity
  in the manual and describe a workaround for those brave enough to try this.
  Fixes #1062.

Author: RyanGlScott

doc/manual/manual.md

@@ -1557,8 +1557,14 @@ control where to look for classes:
   files found in that directory (and its subdirectories) to the class database.
   By default, the current directory is included in the class path.
 
-Most Java programs will only require setting the `-b` flag, as that is enough
-to bring in the standard Java libraries.
+Most Java programs will only require setting the `-b` flag (or the `PATH`), as
+that is enough to bring in the standard Java libraries. Note that when
+searching the `PATH`, SAW makes assumptions about where the standard library
+classes live. These assumptions are likely to hold on JDK 7 or later, but they
+may not hold on older JDKs on certain operating systems. If you are using an
+old version of the JDK and SAW is unable to find a standard Java class, you may
+need to specify the location of the standard classes' JAR file with the `-j`
+flag (or, alternatively, with the `SAW_JDK_JAR` environment variable).
 
 Once the class path is configured, you can pass the name of a class to
 the `java_load_class` function.

intTests/runtests.sh

@@ -36,17 +36,17 @@ fi
 
 # Build the class path. On Windows, Java requires Windows-style paths
 # here, even in Cygwin.
-#
-# Locate rt.jar. This is already a Windows path on windows, so no need
-# to 'cygpath' it.
-JDK=$(support/find-java-rt-jar.sh)
-CP="$JDK"
+CP=""
 # Add our bundled .jars to the class path.
 for i in "$TESTBASE"/jars/*.jar; do
   if [ "$OS" == "Windows_NT" ]; then
     i=$(cygpath -w "$i")
   fi
-  CP=$CP$CPSEP$i
+  if [ -z "$CP" ]; then
+    CP=$i
+  else
+    CP=$CP$CPSEP$i
+  fi
 done
 export CP