tests/hgterm.ti

obsolete: introduce an `_enabled` switch to disable the feature by default

Obsolete markers wide-usage and propagation should be avoided by default until
the obsolete feature is more mature.

This changeset introduce the `_enable` variable and prevent the creation of
obsolete marker if the feature is set to `False` (the default).

More limitation comes in followup changesets.

hgterm,
	am, km, mir, msgr, xenl,
	colors#8, cols#80, it#8, lines#24, pairs#64,
	acsc=``aaffggiijjkkllmmnnooppqqrrssttuuvvwwxxyyzz{{||}}~~,
	bel=^G, bold=\E[1m, clear=\E[H\E[2J, cr=\r,
	csr=\E[%i%p1%d;%p2%dr, cub=\E[%p1%dD, cub1=\b,
	cud=\E[%p1%dB, cud1=\n, cuf=\E[%p1%dC, cuf1=\E[C,
	cup=\E[%i%p1%d;%p2%dH, cuu=\E[%p1%dA, cuu1=\E[A,
	dch=\E[%p1%dP, dch1=\E[P, dl=\E[%p1%dM, dl1=\E[M,
	ed=\E[J, el=\E[K, enacs=\E)0, home=\E[H, ht=\t,
	hts=\EH, il=\E[%p1%dL, il1=\E[L, ind=\n,
	is2=\E[m\E[?7h\E[4l\E>\E7\E[r\E[?1;3;4;6l\E8, kbs=\b,
	kcub1=\EOD, kcud1=\EOB, kcuf1=\EOC, kcuu1=\EOA,
	kdch1=\E[3~, kf1=\E[11~, kf10=\E[21~, kf11=\E[23~,
	kf12=\E[24~, kf13=\E[25~, kf14=\E[26~, kf15=\E[28~,
	kf16=\E[29~, kf17=\E[31~, kf18=\E[32~, kf19=\E[33~,
	kf2=\E[12~, kf20=\E[34~, kf3=\E[13~, kf4=\E[14~,
	kf5=\E[15~, kf6=\E[17~, kf7=\E[18~, kf8=\E[19~,
	kf9=\E[20~, kfnd=\E[1~, kich1=\E[2~, kmous=\E[M,
	knp=\E[6~, kpp=\E[5~, kslt=\E[4~, op=\E[m, rc=\E8,
	rev=\E[7m, ri=\EM, rmacs=^O, rmcup=\E[2J\E[?47l\E8,
	rmir=\E[4l, rmkx=\E[?1l\E>, rmso=\E[m, rmul=\E[m,
	rs2=\E[m\E[?7h\E[4l\E>\E7\E[r\E[?1;3;4;6l\E8, sc=\E7,
	setab=\E[4%p1%dm, setaf=\E[3%p1%dm, sgr0=\E[m,
	smacs=^N, smcup=\E7\E[?47h, smir=\E[4h,
	smkx=\E[?1h\E=, smso=\E[7m, smul=\E[4m, tbc=\E[3g,
	u6=\E[%i%d;%dR, u7=\E[6n, u8=\E[?1;2c, u9=\E[c,