java-wrappers fails ito find java runtimes installed in /opt

[Impact]
java-wrappers failed to find java runtime installed in /opt, which caused all java-based program failed to launch, if the user installed java runtime from Oracle.

apt-cache rdepends java-wrappers
java-wrappers
Reverse Depends:
  freemind
  worldwind
  jajuk
  weka
  umlet
  sweethome3d
  statsvn
  statcvs
  sqlline
  pdfsam
  opticalraytracer
  latexdraw
  jxplorer
  jsymphonic
  jmeter
  jftp
  jeuclid-mathviewer
  jeuclid-cli
  jedit
  jardiff
  jalview
  jabref
  hdfview
  freeplane
  freemind
  freecol
  elki
  electric
  checkstyle
  bnd
  basex
  azureus
  yui-compressor
  libfop-java
  libbatik-java

[Test Case]

UBUNTU RELEASE (cat /etc/lsb-release)
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=12.04
DISTRIB_CODENAME=precise
DISTRIB_DESCRIPTION="Ubuntu 12.04 LTS"

PACKAGES
ii freemind 0.9.0+dfsg-1 Java Program for creating and viewing Mindmaps
ii java-wrappers 0.1.24 wrappers for java executables

When /etc/alternatives/java points to java runtime installed in /opt (example may be /opt/ibm-java-i386-60/bin/java), then in /usr/lib/java-wrappers/jvm-list.sh emply value is assigned to __jvm_alt in following assignment:

__jvm_alt=$(readlink /etc/alternatives/java|sed -n 's/\(\/usr\/lib\/jvm\/[^\/]*\)\/.*/\1/p')

Reason is that bacause sed expression did not match path in /opt/..., no substitution is made, and such sed statement prints pattern space only if substitution is made.

Therefore in /usr/lib/java-wrappers/java-wrappers.sh fgrep in following code always succeeds and JAVA_HOME is set to empty:
 if echo "$DIRS" | fgrep "$__jvm_alt" > /dev/null ; then
     JAVA_HOME="$__jvm_alt"
     java_debug "Picking up the JVM designated by the alternatives system: "
     java_debug " JAVA_HOME = '$JAVA_HOME'"
 else

        # And pick up the first one that works reasonably
     for dir in $DIRS; do
  if [ -x $dir/bin/java ]; then
      JAVA_HOME=$dir
      break;
  fi
     done
 fi

This eventually leads to this abnormal exit:
    if [ "$JAVA_HOME" ] ; then
 # ... omitted ...
    else
 java_warning "No java runtime was found"
 return 1;
    fi

Hence other packages that use java-wrappers, e.g. freemind, experience other failures because java-wrappers failure. In example of freemind, it will not start at all.