build.sh: Support comments in package files (#14)

* build.sh: Support comments in package files

This patch allows the use of hash comments inside patch files.  It's a
little ugly, but it strips comments and collapses all whitespace down to
single space characters between package names.  It handles comments
anywhere in a line, as well.

Was unsure if \ continuation of the long sed line or the inclusion of a
couple of lines of comments explaining what the sed expressions are
doing would be appreciated, so didn't include them in this patch.

* build.sh: whitespace fix

* build.sh: Use sed script for packages files

Broke the sed expressions out of build.sh and put them their own
documented sed script.  This greatly improves readability and avoids
build.sh getting messier.

Broke the substitution command into two separate subs.  The first just
deletes comments, and the second collapses all whitespace into a single
space.  This too is easier to read, and catches a couple of edge cases
that would result it not all whitespace being collapsed.  The result may
still have (one) leading and/or trailing space, which is acceptable.

build.sh

@@ -16,7 +16,8 @@ EOF
 		fi
 		if [ -f ${i}-packages-nr ]; then
 			log "Begin ${SUB_STAGE_DIR}/${i}-packages-nr"
-			PACKAGES=`cat $i-packages-nr | tr '\n' ' '`
+			PACKAGES="$(sed -f "${SCRIPT_DIR}/remove-comments.sed" < ${i}-packages-nr)"
+			PACKAGES="$(sed -e "$sed_expr_packages" < ${i}-packages-nr)"
 			if [ -n "$PACKAGES" ]; then
 				on_chroot sh -e - << EOF
 apt-get install --no-install-recommends -y $PACKAGES
@@ -26,7 +27,7 @@ EOF
 		fi
 		if [ -f ${i}-packages ]; then
 			log "Begin ${SUB_STAGE_DIR}/${i}-packages"
-			PACKAGES=`cat $i-packages | tr '\n' ' '`
+			PACKAGES="$(sed -f "${SCRIPT_DIR}/remove-comments.sed" < ${i}-packages)"
 			if [ -n "$PACKAGES" ]; then
 				on_chroot sh -e - << EOF
 apt-get install -y $PACKAGES
@@ -77,6 +78,7 @@ EOF
 	log "End ${SUB_STAGE_DIR}"
 }
 
+
 run_stage(){
 	log "Begin ${STAGE_DIR}"
 	STAGE=$(basename ${STAGE_DIR})

scripts/remove-comments.sed

@@ -0,0 +1,11 @@
+# Deletes comments and collapses whitespace in ##-packages files
+
+# Append (N)ext line to buffer
+# if (!)not ($)buffer is EOF, (b)ranch to (:)label loop
+:loop
+N
+$ !b loop
+
+# Buffer is "line1\nline2\n...lineN", del comments and collapse whitespace
+s/#[^\n]*//g
+s/[[:space:]]\{1,\}/ /g