Move 'redo --ifchange' into 'redo-ifchange' to match djb's style.

It does simplify the logic of both redo.py and redo-ifchange.py, I suppose.

t/bellow.do

@@ -1,2 +1,2 @@
-redo --ifchange LD yellow.o
+redo-ifchange LD yellow.o
 ./LD bellow yellow.o

t/hello.do

@@ -1,2 +1,2 @@
-redo --ifchange LD hello.o
+redo-ifchange LD hello.o
 ./LD hello hello.o

t/hello.o.do

@@ -1,2 +1,2 @@
-redo --ifchange CC hello.c /usr/include/stdio.h
+redo-ifchange CC hello.c /usr/include/stdio.h
 ./CC hello.c

t/it.do

@@ -1,2 +1,2 @@
-redo --ifchange hello yellow bellow
+redo-ifchange hello yellow bellow
 

t/runtests.do

@@ -1,2 +1,2 @@
-redo --ifchange it
+redo-ifchange it
 ./hello >&2

t/yellow.do

@@ -1,2 +1,2 @@
-redo --ifchange LD yellow.o
+redo-ifchange LD yellow.o
 ./LD yellow yellow.o

t/yellow.o.do

@@ -1,2 +1,2 @@
-redo --ifchange CC hello.c
+redo-ifchange CC hello.c
 gcc -o $3 -c hello.c