Use of invalid property values gives bad error messages

[Dave Abrahams]

I used <link>dynamic in one of my Jamfiles instead of <link>static. Note that the backtrace does not even refer to the line in the Jamfile where this transgression occurred. Pity the poor user who tries to debug this!

X:/common/boost/tools/build/v2/build\feature.jam:432: in validate-value-string from module feature
error: "dynamic" is not a known value of feature <link>
error: legal values: "shared" "static"
X:/common/boost/tools/build/v2/build\feature.jam:316: in expand-subfeatures-aux from module feature
X:/common/boost/tools/build/v2/build\feature.jam:374: in expand-subfeatures from module feature
X:/common/boost/tools/build/v2/build\feature.jam:782: in feature.expand from module feature
X:/common/boost/tools/build/v2/build\property-set.jam:170: in object(property-set)@782.expand from module object(propert
y-set)@782
X:/common/boost/tools/build/v2/build\targets.jam:731: in object(main-target)@577.generate from module object(main-target
)@577
X:/common/boost/tools/build/v2/build\targets.jam:895: in targets.generate-from-reference from module targets
X:/common/boost/tools/build/v2/build\targets.jam:1169: in generate-dependencies from module object(typed-target)@471
X:/common/boost/tools/build/v2/build\targets.jam:1214: in object(typed-target)@471.generate from module object(typed-tar
get)@471
X:/common/boost/tools/build/v2/build\targets.jam:765: in generate-really from module object(main-target)@560
X:/common/boost/tools/build/v2/build\targets.jam:738: in object(main-target)@560.generate from module object(main-target
)@560
X:/common/boost/tools/build/v2/build\targets.jam:895: in targets.generate-from-reference from module targets
X:/common/boost/tools/build/v2/build\targets.jam:1169: in generate-dependencies from module object(alias-target-class)@4
75
X:/common/boost/tools/build/v2/build\targets.jam:1214: in object(alias-target-class)@475.generate from module object(ali
as-target-class)@475
X:/common/boost/tools/build/v2/build\targets.jam:765: in generate-really from module object(main-target)@562
X:/common/boost/tools/build/v2/build\targets.jam:738: in object(main-target)@562.generate from module object(main-target
)@562
X:/common/boost/tools/build/v2/build\targets.jam:255: in object(project-target)@230.generate from module object(project-
target)@230
X:/common/boost/tools/build/v2\build-system.jam:402: in load from module build-system
X:\common\boost\tools\build\v2/kernel\modules.jam:261: in import from module modules
X:\common\boost\tools\build\v2/kernel/bootstrap.jam:132: in boost-build from module
X:\common\boost\boost-build.jam:9: in module scope from module