haddock.mk: Use \{1,\} instead of \+

This works around Mac OS X's sed, which doesn't support \+.
For the record,

    The regex implementation in Mac OS X 10.8 and later is based on a heavily
    modified subset of TRE, http://laurikari.net/tre/

rules/haddock.mk

@@ -10,10 +10,10 @@
 #
 # -----------------------------------------------------------------------------
 
-HADDOCK_VER := $(shell grep "^version:" utils/haddock/haddock.cabal | sed "s/^version: \+//")
-HADDOCK_MAJOR_VER := $(shell echo $(HADDOCK_VER) | sed 's/\([0-9]\+\).\([0-9]\+\).\([0-9]\+\)/\1/')
-HADDOCK_MINOR_VER := $(shell echo $(HADDOCK_VER) | sed 's/\([0-9]\+\).\([0-9]\+\).\([0-9]\+\)/\2/')
-HADDOCK_PATCH_VER := $(shell echo $(HADDOCK_VER) | sed 's/\([0-9]\+\).\([0-9]\+\).\([0-9]\+\)/\3/')
+HADDOCK_VER := $(shell grep "^version:" utils/haddock/haddock.cabal | sed "s/version: *//")
+HADDOCK_MAJOR_VER := $(shell echo $(HADDOCK_VER) | sed 's/\([0-9]\{1,\}\)\.\([0-9]\{1,\}\)\.\([0-9]\{1,\}\)/\1/')
+HADDOCK_MINOR_VER := $(shell echo $(HADDOCK_VER) | sed 's/\([0-9]\{1,\}\)\.\([0-9]\{1,\}\)\.\([0-9]\{1,\}\)/\2/')
+HADDOCK_PATCH_VER := $(shell echo $(HADDOCK_VER) | sed 's/\([0-9]\{1,\}\)\.\([0-9]\{1,\}\)\.\([0-9]\{1,\}\)/\3/')
 HADDOCK_VERSION_STRING := $(shell echo $$(($(HADDOCK_MAJOR_VER) * 1000 + $(HADDOCK_MINOR_VER) * 10 + $(HADDOCK_PATCH_VER))))
 
 define haddock  # args: $1 = dir,  $2 = distdir