Updated gdbclient path support.

Now gdbclient accepts a fully qualified pathname for EXEs, which it will
not modify, or a relative pathname, to which it will prefix
"/system/bin".  As an example, each of the following now works.

Fully qualified:
adb shell gdbserver :5039 /system/bin/ping
bg
gdbclient /system/bin/ping :5039 /system/bin/ping

Relative:
adb shell gdbserver :5039 /system/bin/ping
bg
gdbclient ping :5039 /system/bin/ping

Change-Id: I1e4c9fca64c4fbc52c255271cc7f83f35c258509

envsetup.sh

@@ -996,6 +996,9 @@ function gdbclient()
        local EXE="$1"
        if [ "$EXE" ] ; then
            EXE=$1
+           if [[ $EXE =~ ^[^/].* ]] ; then
+               EXE="system/bin/"$EXE
+           fi
        else
            EXE="app_process"
        fi