Add 'VCS' key

Spec files have a lot of metadata about a project.  However one of the
most key components is the upstream version control system which was
notably lacking.

Resolve this by adding a "VCS" key.  There is no specification
for contents of this key, given that the set of version control
systems (and features thereof) are not well-defined.  However,
recommendations are:

 * git: This URL should be in a form that can be passed to "git clone",
   with the additional feature that an optional fragment identifier "#foo"
   denotes a branch or tag.

build/parsePreamble.c

@@ -33,6 +33,7 @@ static const rpmTag copyTagsDuringParse[] = {
     RPMTAG_VENDOR,
     RPMTAG_ICON,
     RPMTAG_URL,
+    RPMTAG_VCS,
     RPMTAG_CHANGELOGTIME,
     RPMTAG_CHANGELOGNAME,
     RPMTAG_CHANGELOGTEXT,
@@ -700,6 +701,8 @@ static int handlePreambleTag(rpmSpec spec, Package pkg, rpmTag tag,
     case RPMTAG_URL:
     case RPMTAG_DISTTAG:
     case RPMTAG_BUGURL:
+    /* XXX TODO: validate format somehow */
+    case RPMTAG_VCS:
 	SINGLE_TOKEN_ONLY;
 	headerPutString(pkg->header, tag, field);
 	break;
@@ -884,6 +887,7 @@ static struct PreambleRec_s const preambleList[] = {
     {RPMTAG_GROUP,		1, 0, LEN_AND_STR("group")},
     {RPMTAG_PACKAGER,		0, 0, LEN_AND_STR("packager")},
     {RPMTAG_URL,		0, 0, LEN_AND_STR("url")},
+    {RPMTAG_VCS,        0, 0, LEN_AND_STR("vcs")},
     {RPMTAG_SOURCE,		0, 0, LEN_AND_STR("source")},
     {RPMTAG_PATCH,		0, 0, LEN_AND_STR("patch")},
     {RPMTAG_NOSOURCE,		0, 0, LEN_AND_STR("nosource")},

tests/rpmgeneral.at

@@ -241,6 +241,7 @@ TRIGGERTYPE
 TRIGGERVERSION
 URL
 V
+VCS
 VENDOR
 VERBOSE
 VERIFYSCRIPT