[Rd] save() file size (PR#13816)

[Mike.Lawrence at dal.ca]

Full_Name: Mike Lawrence
Version: 2.9.0
OS: OS 10.5.7
Submission from: (NULL) (208.98.203.100)


When using save() I notice that sometimes saving smaller objects yield larger
file sizes.

x=data.frame(
	expand.grid(
		id=factor(1:1000)
		,trial=1:24
		,cue=factor(1:3)
		,flank=factor(1:4)
	)
)
save(x,file='temp1.Rdata') #about 20KB
y=x[x$id!='1',]
save(y,file='temp2.Rdata') #>500KB