2014-01-22: allow setting alternate names for guile and python3 in configure.

allow setting alternate names for guile and python3 in configure.

diff --git a/Makefile.am b/Makefile.am
--- a/Makefile.am
+++ b/Makefile.am
@@ -14,7 +14,7 @@ ChangeLog :
 
 .INTERMEDIATE: input.in.intermediate
 input.in.intermediate: ${wisp_SOURCES}
-	@abs_top_srcdir@/bootstrap.sh @abs_top_srcdir@
+	@abs_top_srcdir@/bootstrap.sh @abs_top_srcdir@ @guile@ @python3@
 
 .PHONY: test.sh
 test.sh : wisp.scm runtests.sh
diff --git a/bootstrap.sh b/bootstrap.sh
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -7,7 +7,21 @@ else
     srcdir="$1"
 fi
 
-diff=$(python3 ${srcdir}/wisp.py ${srcdir}/wisp-guile.w > 1 && guile 1 ${srcdir}/wisp-guile.w > 2 && guile 2 ${srcdir}/wisp-guile.w > wisp.scm && diff 2 wisp.scm && echo success)
+# Bootstrap wisp-guile with wisp.py
+if [[ x"$2" == x"" ]]; then 
+    guile="guile"
+else
+    guile="$2"
+fi
+
+# Bootstrap wisp-guile with wisp.py
+if [[ x"$3" == x"" ]]; then 
+    python3="python3"
+else
+    python3="$3"
+fi
+
+diff=$(${python3} ${srcdir}/wisp.py ${srcdir}/wisp-guile.w > 1 && ${guile} 1 ${srcdir}/wisp-guile.w > 2 && ${guile} 2 ${srcdir}/wisp-guile.w > wisp.scm && diff 2 wisp.scm && echo success)
 if [[ ! x"${diff}" == x"success" ]]; then
     echo "failed to bootstrap wisp.scm. diff: " ${diff}
     exit 1
@@ -16,7 +30,7 @@ echo "successfully bootstrapped wisp.scm
 echo preparing the reader: wisp at the REPL
 echo parsing the spec file...
 mkdir -p language/wisp
-guile wisp.scm ${srcdir}/wisp-reader.w 2>/dev/null > language/wisp/spec.scm \
+${guile} wisp.scm ${srcdir}/wisp-reader.w 2>/dev/null > language/wisp/spec.scm \
     && echo ...precompiling the spec file... \
     && guile -L . -s language/wisp/spec.scm \
     && echo ...succeeded \
diff --git a/configure.ac b/configure.ac
--- a/configure.ac
+++ b/configure.ac
@@ -9,6 +9,7 @@ AC_ARG_VAR([guile], [How to call GNU Gui
 AC_CHECK_TARGET_TOOL([guile], [guile], [no])
 AS_IF([test "x$guile" = "xno"],
       [AC_MSG_ERROR([cannot find GNU Guile.])])
+AC_ARG_VAR([python3], [How to call Python 3.])
 AC_CHECK_TARGET_TOOL([python3], [python3], [no])
 AS_IF([test "x$python3" = "xno"],
       [AC_MSG_ERROR([cannot find Python 3 which is required for bootstrapping.])])