beeversion: Add prefix char to print formatted extraname and extraver…

…sion

To prefix extraname and extraversion just add the prefix char before
e or x in the formatstring: e.g.

pkg_subname-1.0_extra1-0

%-e =>  -extra1
%_e =>  _extra1

%-x =>  -subname
%_x =>  _subname

This is only supposed to be used with '-' or '_' even if you may use other
chars here. But the behavior may change in future version. Only '_' and '-'
are stable for the moment.

src/bee_version_output.c

@@ -137,6 +137,20 @@ void print_format(char* s, struct beeversion *v, char *filter_pkgfullname)
                         printf(".%s", v->arch);
                     break;
             }
+            if (*p) {
+                switch(*(p+1)) {
+                    case 'x':
+                        if (*(v->subname))
+                            printf("%c%s", *p, v->subname);
+                        p++;
+                        continue;
+                    case 'e':
+                        if (*(v->extraversion))
+                            printf("%c%s", *p, v->extraversion);
+                        p++;
+                        continue;
+                }
+            }
             continue;
         } /* if '%' */